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Article Outline
Chapter 1
Introduction to PCB Assembly
Chapter 2
Steps of PCB Assembly Process
Chapter 3
PCB Assembly Cost Breakdown and Estimation
Chapter 4
Effective Ways for PCBA Cost Reduction While Maintaining Quality
Chapter 5
How to Choose a PCB Assembly Partner and Metrics Evaluation
Chapter 6
Conclusion and How Circuitsify Can Help
PCB Assembly (PCBA) Services: The Complete Guide to Choose your PCB Assembly Manufacturer
In everything we do, electronics is a major component of our daily lives. All our smartphones, gadgets and even cars have built-in electronic parts. At the core of any electronic manufacturing services consists of the printed circuit board assembly (PCBA).
Many people are aware what PCBs are when they see them. They consist of mini green chips that are being covered in lines and copper parts that can be viewed at the center of any gutted electronic equipment. Designed with fiberglass, copper lines and other metal components, these boards are attached together using epoxy and an insulated solder mask. This mask is the source where the green color is found.
Have you ever wondered those PCBs with components are solidly attached during the electronic contract manufacturing? These pieces are not simply decorations of a PCB board. A sophisticated printed circuit board that provides its full functionality should have all the tiny components that it needs. A PCB with mounted components is called PCB assembly or simply PCBA. To fully understand how the PCBA process works from scratch to its completion, please read in detail the guide below.
Chapter 1. Introduction to PCB Assembly
1.1 What is PCB Assembly
A printed circuit board assembly, also known as PCBA, consists of soldering or how the electronic parts are being assembled to a printed circuit board (PCB). Initially, a circuit board before assembling the electronic parts is called PCB. After the electronic components have been soldered, the board can now be called printed circuit assembly (PCA) or printed circuit board assembly (PCBA).
1.2 Process of PCB Assembly
The PCBA process always begins with the base, which is the basic unit of the PCB. It has different layers. Each has a vital role in how the final PCB works. Below are the alternating layers.
The substrate acts as the PCB base material that provides its rigidity. With regard to copper, a thin layer of conductive copper foil is combined with every functional side of the PCB. On one side, a single-sided PCB is added or on both sides if a dual-sided PCB is necessary. This serves as the layer of copper traces.
Above the copper layer, the solder mask is found. This provides every PCB the green color feature. It is in-charge of insulating the copper traces from accidentally getting in contact with other conductive materials, which may lead to a short. Simply, the solder helps to keep everything in place. The solder mask holes are where solder is placed to attach the parts to the board. Solder mask is a critical process for the smooth manufacturing of PCBA since it ends soldering to occur on unnecessary parts and prevent a short. The white silkscreen is used as the final layer on a PCB board. This layer makes the PCB labels through characters and symbols. It is used to identify the function of each part on the PCBA.
1.3 Cost Estimation for PCB Assembly
Many factors are being considered by the designers in creating better estimates on the manufacturing cost of a printed circuit board assembly (PCBA) at the initial stage of concept design. All activities are laid out, quantified in detail and allocating the costs based on the amount and type of tasks necessary for the printed circuit board assembly. The activity costs are calculated based on the task charts, worksheets, and cost build-up range. Designers can identify potential issues that can impact substantial cost and do early preventive measures to reduce the costs. Getting early manufacturing cost data at the design cycle, these can improve target productivity and the estimated manufacturing costs. Using the activity charts will best present an illustration in the application of the cost estimated procedures.
1.4 Effective Ways to Reduce Cost, Maintaining Quality, and Choosing a Manufacturer
Any manufacturing enterprise should be careful and diligent in checking any revisions created to the PCB assembly. Looking for better options to enable PCB assembly services more price-efficient and cost-effective is highly advised than simply cutting down costs. Generally, this can be done. To assist you in increasing your profitability and achieving your desired earnings, below are simple saving tips to consider while keeping the quality of the PCB assembly.
Smart design. The design and planning processes that are needed in the printed circuit board assembly are the best ways to reduce needless spending. Using strategic engineering methods for PCBA, this can lead to using fewer parts that will minimize the cost per PCB assembly. In the long run, this brings significant savings to the company.
Establishing rapport. Building a strong relationship with your parts suppliers is certainly more cost-efficient compared to opening a huge range of products. Once you have a good rapport with your parts supplier, you can surely bargain for better deals and savings, and be given the chance to negotiate for good discounts for early payments for hiring its PCB assembly services.
Prevent hefty penalties. Always keep up with standard PCB assembly requirements. Are you planning to seek offshore your PCB assembly services? Think again. Many overseas contract manufacturers are appealing to smaller enterprises as they advertise cheap PCB assembly services. Whenever the price is too good to be true, you may fall prey into it. Oftentimes, these PCB assembly service companies have the risk of providing counterfeit parts without your knowledge that do not comply with the American industry standards. The use of these parts in your PCBA requirements could put you in a situation of being fined or filed a lawsuit for the problematic part that can bring serious defects or malfunctions in your PCB.
Repair or replace. If any of your PCBAs encounter a problem, you might be tempted to provide a customer with a warranty replacement instead of troubleshooting the problem and repairing it. In reality, the latter is more affordable and cost-efficient.
Outsourcing. Employing a contracted PCB assembly services manufacturer may be more expensive initially. However, you can partner to a team of experts without the need to pay for their salaries and have access to sophisticated equipment without purchasing or maintaining them.
Saving your budget on printed circuit board assembly should never compromise the product quality for your customers. Using the simple tips cited, you can reduce costs while helping your customers happy with your boards and PCB assembly services.
Chapter 2. Steps of PCB Assembly Process
- 2.1 Solder Paste Stenciling
- 2.2 Pick and Place
- 2.3 Reflow Soldering
- 2.4 Inspection and Quality Control
- 2.4.1 Manual checks
- 2.4.2 Automatic optical inspection
- 2.4.3. X-ray inspection
- 2.5 Through-Hole Component Insertion
- 2.5.1 Manual soldering
- 2.5.2. Wave soldering
- 2.6 Final Inspection and Functional Test
A PCB is a baseline when wiring and supporting the surface-mounted or socketed parts in electronics. In circuits, where you have to look for conductive traces such as computer processes, these PCBs are created using the photolithographic methods. This is similar to how the conductive lines are designed for the processors but on a much higher level.
In a printed circuit board assembly, it has to undergo several stages. However, it is necessary that in every stage it should be thoroughly checked so it will work together towards an integrated overall process. In every stage of the PCB assembly, compatibility is crucial to get to the next level successfully.
Feedback is vital from the output to the input while maintaining the highest quality. Through this, any issues are easily identified and provide the necessary adjustments accordingly. Below are the actual PCBA processes.
2.1 Solder Paste Stenciling
The initial step of a PCB assembly is putting a solder paste to the PCB. This method is similar when you are screen-printing a shirt. The only difference is that the mask, a thin, stainless-steel stencil is positioned at the top of the PCB. This enables the PCB assembly services companies to put the solder paste to the specific places of the newly created PCB. These parts are where the components will be installed in the finalized PCBA.
The solder paste is characterized as a grayish matter made of mini metal balls of metal, also called solder. The components of these miniature metal balls consist of 96.5% Pb, 3% Ag, and 0.5% Cu. The solder paste combines solder with a flux. The latter is a chemical used in aiding the solder to melt and easily bond to a surface. Solder paste looks like a gray paste that should be applied to the PCB assembly accurately at the right places and sufficient content.
In a commercial PCBA production line, mechanical equipment is used to put the PCB and solder stencil in place. The applicator is needed to place the solder paste on the desired areas at the appropriate amounts. The equipment is used to evenly distribute the paste in the stencil, where its application is equally spread to each hole. After taking out the stencil, the solder paste is kept at the intended locations.
2.2 Pick and Place
Following the application of the solder paste to the board, the PCBA method shifts to the pick-and-place equipment, a robotic tool is used to place the surface mount parts (SMD) on a designated PCB. SMD is vital for most non-connector components used on PCBAs today. These SMDs are being soldered on the board surface succeeding the printed circuit board assembly process.
In the past, this was a manual approach using a pair of tweezers. It is where the PCB assembly services companies needed to pick and place the parts using their hands. Currently, this process has been automated to help PCB assembly manufacturers in doing the task accurately. This development contributed to producing more accurate and consistent machines than those performed manually. Although human labor can still work quickly, external factors like fatigue and eyestrain are experienced after a few hours while assembling the tiny PCBA components. Automated machines can be used anytime any fatigue.
The machine begins the pick-and-place process by getting the board using a vacuum grip and transferring it to the station. The robot works on the PCBA at the station and applies the SMTs to the printed circuit board assembly surface. These parts are positioned above the soldering paste in pre-programmed areas.
2.3 Reflow Soldering
After the solder paste and SMT are installed in their proper places, they need to stay there until they are completely pasted. The solder paste has to solidify, integrating the board components. PCB assembly services are held through a method known as ‘reflow.’
After the pick and place procedure is finalized, the PCBA board is moved to a conveyor belt. This belt works through a huge reflow oven similar to a commercial pizza oven. It consists of several heaters that slowly heat the board to temperatures ranging from 250-degrees Celsius or 480-degrees Fahrenheit. This is very hot and can melt the solder in the solder paste.
When the solder is melted, the PCB remains in the oven. Then it has to pass through the cooler heaters, enabling the melted solder to cool down and solidify in a controlled way. This brings a permanent solder joint to attach the SMDs to the PCB.
Many PCBAs need special requirements during reflow, particularly for the two-sided PCB assembly. Two-sided PCB assembly requires separate stenciling and reflowing in every side. Initially, the side with fewer and mini components is stenciled, positioned and reflowed, then the other side follows.
2.4 Inspection and Quality Control
After soldering the surface mount components in place, it undergoes the reflow method, but it is not enough for printed circuit board assembly completion, where the assembled PCB should be tested for its functionality. Oftentimes, any activity in the reflow process leads to poor connection quality or a full lack of connection. Experiencing shorts is a very common side effect of the testing process. There may be instances of misplaced parts that are sometimes attached to the wrong circuit.
Analyzing the errors and some misalignments include different inspection processes. The most common PCBA methods are:
2.4.1 Manual checks
Although there are trends and automated and smart manufacturing systems used in the PCB assembly process, manual checks are used in the PCBA. For smaller batches, a manual visual inspection by the designer is an effective way of ensuring the PCB quality after the reflow process. However, this method has become impractical, obsolete and inaccurate with the increased number of boards for inspection. Human labor checking has shown limitations in small components after more than an hour causing optical fatigue and less accurate inspection.
2.4.2 Automatic optical inspection
This type of inspection is the preferred method for larger PCB assembly batches. AOI, an automatic optical inspection equipment, employs several high-powered cameras when viewing the PCBs. These cameras are positioned at various angles to analyze the solder connections. Different qualities of solder connections are reflecting light in various ways, enabling the AOI to identify a poor quality solder. The AOI functions at a very high speed, processing quickly large batches of PCBAs in a relatively reduced period.
2.4.3 X-ray inspection
X-rays are also used as an inspection method. Although is it not a commonly used system, it is widely used in complex or layered PCBAs. The x-ray helps a viewer to see through hidden layers and visualize closely lower layers with potential problems that cannot be seen by the naked eye. When the board malfunctions, it is usually sent back for rechecking, reworking or totally scrapped/disposed of.
If in the inspection there are errors seen, the next step is testing the part to ensure that it functions as what it is supposed to do. This includes checking the quality of the printed circuit board assembly connections. PCB assembly that need further programming or calibration undergo more tests to validate its functionality.
These inspections are common after the reflow process to identify any potential issues. The regular checking is vital to correct errors and provide possible solutions immediately, which is advantageous to both the manufacturer and the designer in saving time, labor and BOMs.
2.5 Through-Hole Component Insertion
Based on the board type under PCBA, the PCB involves different parts aside from the basic SMDs. These may include plated-through-hole (PTH) parts.
A PTH is a type of hole in the PCBA that is fully plated in the board. PCB assembly parts need these holes to pass a signal from one board side to the other. In this instance, the soldering paste will not work, as the paste will pass through the hole and not attach.
Instead of using soldering paste, PTH components need a more advanced soldering method in the PCB assembly process:
2.5.1 Manual soldering
Manual through-hole insertion is a basic process. In general, an individual at one station will be assigned to insert one part into a designated PTH. Once it is done, the PCB is sent to the next station, where another worker will be inserting a different part. This continues for every PTH that will be inserted. It can be a tedious process, which is based on the number of PTH components that need to be inserted in a printed circuit board assembly cycle. Most firms try to avoid designing with PTH components because of this. However, PTH components are still widely used in PCB assembly designs.
2.5.2 Wave Soldering
It is an automated approach of manual soldering that works in a very different way. After the PTH component is positioned, the PCB is placed on another conveyor belt. In this case, the belt passes through a sophisticated oven using a wave of molten solder to wash over the board’s bottom part. This solders all of the available pins on the PCB bottom instantly. This soldering type is difficult to use for double-sided PCBAs. The reason behind is that soldering the whole PCB side would not render the desired activity for any sensitive electronic part.
After this soldering method is completed, the PCB assembly goes to the final inspection. In some cases, it has to rerun the previous process whenever the PCB requires additional parts or another side has to be assembled.
2.6 Final Inspection and Functional Test
Once the soldering of the PCBA process is finalized, the last inspection process involves testing the PCB assembly functionality. This type of inspection is called ‘functional testing.’ The test validates the printed circuit board assembly at various paces, simulating the common circumstances where the PCB will be used. The power and simulated signals pass through the PCB in this test as testers observe the PCBA’s electrical features.
Chapter 3. PCB Assembly Cost Breakdown and Estimation
- 3.1 Bare Board Cost
- 3.1.1 Raw Material Type and Thickness
- 3.1.2 Board Size
- 3.1.3 Layer Count
- 3.1.4 Quantity and Lead Time
- 3.2 Component Cost
- 3.3 Printed Circuit Board Assembly Cost
- 3.4 Quality Control, Inspection, and Testing Cost
- 3.4.1 Manual visual inspection
- 3.4.2 Automatic optical inspection
- 3.4.3 X-ray inspection (AXI)
- 3.4.4 In-circuit testing
- 3.4.5 Functional testing
As part of the continuous printed circuit board assembly’s development, the electronic device designs are being upgraded with miniaturization as the latest trend of the innovation process. Every manufacturer seeks to produce a user-friendly, very handy, and compact PCBA with features suitable for it. The range of printed circuit boards comes from simple single layer rigid layouts to more complex multi-layered PCB assemblies. This led to most of the electronic manufacturers to look for a cost-effective and excellent quality PCB assembly. Below are components that should be factored in when calculating the printed circuit board assembly cost and PCB assembly services.
The most basic factors are the raw material cost, labor cost, PCBA facilities and PCB assembly equipment overhead. Also, there are chemical procedures needed in the PCB assembly services, including the wastewater management and securing other permits that are needed when estimating for the final cost for printed circuit board assembly among manufacturers. With all these essential factors to consider, the PCB assembly cost and PCB assembly services have four components such as bare PCB cost, parts costs, assembly cost, and testing expenses.
3.1 Bare board cost
In determining the bare printed circuit board assembly cost, this involves the price, quality, and delivery time of the raw materials, which focuses on their type and thickness, PCB size, and layer count.
3.1.1 Raw Material Type and Thickness
When it comes to PCB types, there are two different types such as rigid PCB and flex PCB. Flexible PCB assembly’s cost is more expensive compared to the rigid PCB board. For the latter, many material types may be available for use to produce a PCB. The most basic is called FR-4. FR-4 consists of a fiberglass and material combined together with an epoxy resin known for its fire-resistant features. Other types include higher temperature FR-4, polyimide, hybrid capable, high copper weight, and flex PCBs that may be chosen to produce high copper weight, hybrid capable PCBs or other types. In general, the most basic material thickness is 0.062-inch. The careful selection of the different material types and thicknesses has a critical effect on the manufacturer’s PCBA price.
3.1.2 Board Size
The printed circuit board’s size is a huge factor that contributes to the PCB assembly services’ production cost. A bigger board size means you need more raw materials to use. This is a vital factor that can impact the overall cost of printed circuit board assembly production. In some instances, based on the client’s specifications, the PCB is built in distinct requirements and this can be costly. In most cases, one dimension is better compared to the other. At times, clients are very particular about their panel requirements. A panel is a larger printed circuit board that has many mini boards that should be divided before using them. Automated printed circuit board handling equipment usually encounters issues with smaller boards, especially when putting several boards together at once, although the process can speed up if necessary. A panel is a vital raw material to create a printed circuit board assembly. The printed circuit board size or the space of the “real estate” it employs up on a panel is a significant factor in estimating the cost/price. It may look simple but, in reality, it can be a complicated thing. For instance, although the dimensions require a PCB that uses less real estate, it may be higher in cost when producing it. The reason behind is the overall panel size needed to manufacture the board. One dimension is more suitable for one panel compared to the other. Let’s take an example, we have two parts with exactly similar total square inches per board. The first is 2-inch x 6-inch while the second is 3-inch x 4-inch. A standard production panel for a PCBA can have more of the 3-inch x 4-inch board as compared to the 2-inch x 6-inch board. So the cost per board would be reduced in the 3-inch x 4-inch board.
3.1.3 Layer Count
The number of layers is a cost-determining factor. Single-sided or double-sided PCBAs are of the same cost to produce. However, multi-layer PCBAs create additional costs in the materials and manufacturing process. Generally, moving to a four-layer PCB from a two-layer PCB assembly can make the price to double. Adding more layers to a multi-layer project requires additional cost but the price increase related to putting more layers is not as obvious. For example, the cost to go from 4 layers to 6 layers may represent a 50% increase as opposed to the 100% increase incurred when shifting from a 2-layer to a 4-layer PCB assembly. In essence, adding layers to the production process will incur an added cost. More layers in the printed circuit board assembly are one factor that is calculated to identify the total PCBA cost. Whether it is a single layer, double layer, quadruple layers or multi-layer printed circuit boards, the prices variation is dependent on the number of raw materials.
3.1.4 Quantity and Lead Time
Quantity and lead time are important in identifying the estimated PCB assembly services cost. You can’t expect that every piece used in the prototyping stage will be as is during the mass production stage. In the prototype or small batch production, there is a required added engineering cost, such as the costs of processing file, stencil, changing SMT line, etc. As a rule of thumb, when smaller quantity and shorter lead time are requested by the client, the cost per unit is usually higher. In terms of quantity, most manufacturers provide a minimum cost for every order. For instance, if you only need 10 pieces for your project, the minimum order cost will require you to pay 20 pieces. As the quantity increases the cost per board is reduced until the minimum manufacturing cost is achieved. Quantity is a critical factor when identifying the PCB assembly cost drivers. Bulk orders are more efficient for the PCB assembly services providers in offering great discounts as they can increase the production level aside from reducing the product cost. Some manufacturers will provide higher quantity discounts but deliver smaller quantities over time. For example, a 500-piece order may be placed with 100 pieces delivered each month until the order has been completely fulfilled. In this case, the manufacturer achieves manufacturing efficiency by producing all 500 pieces at the same time and the customer achieves cash flow efficiency by only paying for the product that has been delivered. In terms of lead time, the old adage, “Time is money,” rings a bell for PCB assembly services providers. The faster a project needs to be produced means it will be more costly – usually between 30% and 200% more. For a PCB assembly manufacturer, there are real costs involved with prioritizing new projects more than the currently existing task. Some of the costs are reflected in the total pricing.
3.2 Component Cost
Based on the negotiated terms between the customers and their EMS partners, the customers either provide all the components or the EMS partner buys the component on behalf of its clients in the turnkey electronic manufacturing services case. When it comes to the electronic component sourcing of a branded part from an authorized dealer, e.g., Mouser/Digikey/etc., it is commonly more expensive than a generic part sourced from the local market. To save cost in the PCBA component sourcing without potentially compromising the final product’s quality, usually, the branded components are the only ones used for the critical parts, e.g., microprocessor or microcontroller, and can replace the rest with generic parts from the local shop.
The cost component can be calculated based on the complete project’s bill of materials (BOMs) list. Based on the customer’s BOM list, the purchasing department of the PCB assembly services company will inquire about the PCB bare board, electronic parts, etc. At times, PCB assembly costs and engineering costs will be incurred in the initial quotation. This covers about 5% of the material loss when buying the components, including the reason for the material loss, such as resistance and capacitance disk loading material and SMT chip.
3.3 Printed Circuit Board Assembly Cost
When we discuss the PCB assembly cost, several factors should be considered such as drill size and count, assembly methods, and technology used (e.g. soldering). When the structure of PCBA began to use complex parts over time, the packaging technology adopted significant production processes to provide added utilities and functionalities. To meet the changing needs for the new complex forms of packaging for the semiconductor industry, several integrated circuits (IC) were created and classified depending on their mounting position.
In general, the PCB assembly cost is directly proportional to the number of drill holes on the board, which can be soldered using various assembly methods, e.g. surface mount technology (SMT) or through-hole, along with different surface finish types, such as Hot Air Solder Leveling (HASL) or Lead Free (Pb-free) and RoHS-compliant. The total drill count is grouped accordingly by the types of solder pads for SMT parts, through-hole components, and integrated circuits (ICs). Each of the component’s lead is connected to its corresponding solar pad and every drill is accounted for separately based on the specific PCB solder joints and processes. Basically, a solder pad is seen as one point and IC solder joints are identified by their feet numbers. The basic surface finish type is hot air solder leveling and any lead-free or RoHS-compliant processing contributes to the additional PCB assembly services overhead. When a double-sided PCB assembly is necessary, this can also increase the total PCBA cost. At the same time, the total number of holes that need to be drilled and their sizes in the PCB should be factored in the printed circuit board assembly’s price calculation. The price percentage increases based on the total drilled holes. This includes the manufacturing customization process while finalizing the final numbers, small hole sizes and the total panels drilled at one time.
3.4 Quality Control, Inspection, and Testing Cost
In the assembly process, many errors can occur on a PCB assembly. Misaligned components are common. Incomplete solder connections can be found. An excess solder can bring circuits or cause shorts. To optimize the PCB’s final yield and its ultimate reliability, each PCB has to pass through strict inspection and testing as per its specific design and performance. For PCB assembly services providers, inspection and testing are crucial for their quality control measures. The related cost is dependent on different types of testing and inspection methods. There is no one-size fits all process for all cases. Generally, the PCB assembly cost based on quality control is mainly affected by the time needed and direct labor cost used to do this, along with other equipment as part of the overhead cost for testing, such as utility, maintenance, and depreciation, etc. The most common inspection and testing methods used in the industry are as follows:
3.4.1 Manual visual inspection
In the past, when printed circuit board assemblies were basically simple, built with few parts and solder attachments, manual visual inspection (MVI) was widely used to spot placement mistakes and solder issues. However, in the long run, this inspection method faced some drawbacks, as human labor is not suitable for this kind of repetitive activity. Most inspectors easily get tired or find the job boring. Some defects are not thoroughly checked or missed with problematic boards not easily seen in the process and they become very expensive to fix or can no longer be fixed.
3.4.2 Automated optical inspection
Automated optical inspection (AOI) is another PCB visual inspection type. In this system, one or multiple still or video cameras are used in the board scanning. The board can be lighted at different angles as the equipment captures images to create the board picture. The process compares the taken images with what the board should appear on a ‘golden board’ or design’s specifics. In this type of inspection, it can be used to check nodules, scratches, and stains, including dimensional defects like open circuits, shorts, and solder thinning. Also, it can spot wrong, missing or skewed parts. This can be carried out with greater accuracy compared to the human inspectors. The new 3D AOI machine checks component height, any defect of the traditional 2D equipment, which employs multi-angled colored lighting, and side-angle cameras. The 2D tools are commonly used for height-sensitive machines such as BGAs and leaded parts, which usually bring unreliable results. Through 3D inspection, this enables the manufacturer to identify coplanarity on height-sensitive devices with ease, although at times shadowing may cause issues on some PCB assembly layouts.
As for AOI benefits, it is a popular and acceptable technology. It is used to spot many common PCB issues. It can be used inline at some parts in the printed circuit board assembly manufacturing method. Some of its disadvantages include its limited line of sight such as the inability to check hidden connections in the BGAS and other systems. It is not reliable when inspecting compact and loaded boards, especially those with hidden or shadowed parts and connections.
3.4.3 X-ray inspection (AXI)
An x-ray inspection tool, automated (AXI) or manual, can identify the solder joints underneath the parts and easily detect defects in the joints that may not be seen using an AOI. Materials can absorb x-rays in the right amount with their atomic weight. Materials with heavier elements have the ability to absorb more x-rays while the lighter elements have higher transparency to x-rays. Solders with heavy elements include tin, silver, bismuth, lead, and indium. Examples of PCBA materials made of lighter elements are carbon, oxygen, aluminum, silicon, hydrogen, sodium, and copper. During x-ray inspection, solder can be seen quickly while in most packages like the PC board substrate, silicon ICs and component leads cannot be detected easily. Compared to the light used in AOI, x-rays are not being reflected. What they can do is to pass through the materials and build an image on the other side.
X-ray inspection can be used to “see” through ICs such as BGAs that are connected underneath. Using x-rays, no shadowing is required so these can detect very complex, densely packed printed circuit boards. This type of inspection offers an internal image of the solder joints, showing bubbles usually unable to see using AOI. Also, x-ray systems can view the solder joint heels that are hidden to AOI after being masked by the leads. X-ray inspection advantages are its ability to see the chip packages that have underneath connections. It can check densely packed PCBs and offer necessary inspection of the solder joints. For its disadvantages, this new technology is not yet well understood. This inspection may only be applicable in cases where BGAS, CSPs and other related packages are employed or whenever the board density is way above the AOI’s capacity.
3.4.4 In-circuit testing
In-circuit test tool ensures each part is accurate and in the right place. In ICT, this looks into a populated printed circuit board assembly, identifying shorts, opens, resistance, capacitance, and other potential issues. It is carried out with a bed-of-nails test fixture or using a flying probe setup. The bed-of-nails tester consists of a range of mini, spring-loaded pogo pins. Each pin is attached to a node in the device under test (DUT) circuitry. Contact is performed with hundreds or more individual test points within the DUT circuitry when being pressed in the pins. A bed-of-nails fixture is expensive to create and hard to change. These fixtures cannot test densely populated PCBs. In-circuit testing, this cannot be used to test the board’s functionality. ICT assumes that a well designed and assembled PCB should function well. ICT advantages include identifying defects like solder shorts, lacking components, inaccurate parts, and open connections. It carries out tests without applying power to the DUT to prevent potential damage. Its disadvantages include having expensive text fixtures (bed of nails) or costly detailed programming (flying probe). Continuity using connectors is not tested making connector problems not easily spotted.
3.4.5 Functional testing
In testing the PCB assembly’s functionality, a tester is used to the PCB using its edge connector or a test-probe point. Functional testing copies the PCB’s final electrical component. Functional testers are usually as distinct as the products they are testing. But PCB assembly services providers try to standardize the process to maintain the costs in check. The overall tester system comprises of a cabinet, a DUT interface, cabling to connect all of the equipment, a central processing unit, and monitors. Hardware may vary according to the DUT and the environment where it will be used, which involves instrumentation and power supplies. The software is used as the operating system, including the test executive and tool sets. Functional testing is designed for the DUT so it needs an investment with sufficient money and time to succeed.
Despite its benefits, functional testing is not perfect. It needs variability, which involves identifying how much of the printed circuit board assembly will be tested, what inputs or stimuli are required, defining the target results and providing the testing parameters. With PCB assembly variability, functional testing is very complex in use. Its advantages include identifying functional issues on the PCB, providing the DUT power use during operation, and checking potential problems with the digital and analog circuitry. The functional testing disadvantages involve being expensive where its programming needs an understanding of the DUT and how it works. It uses costly high-speed instrumentation to describe signals from the DUT. Also, the carried out testing through connectors is prone to reliability issues since connectors may wear anytime.
Chapter 4. Effective Ways for PCBA Cost Reduction While Maintaining Quality
For business owners who only seek low prices while neglecting PCB assembly quality, most of their projects are likely to fail brought by poor quality printed circuit board assemblies.
Printed circuit board assembly methods are evolving to reduce assembly cost, attract more businesses, and be more profitable. One factor to consider in PCB assembly services is price, which varies from one assembler to another. It is highly advised to strike a balance between printed circuit board assembly quality, customer service, and cost. The most important thing to do is to adjust your circuit design to lower the assembly cost and identify the right partner with the best overall PCB assembly service that is within your budget. Below are four effective means to cut down assembly cost with the assurance of high-quality PCB.
4.1 Optimize the bare PCB schematic design with the goal of reducing the cost.
The initial step prior to the actual manufacturing is to identify whether your circuit boards can be easily implemented. This is also called checking for design-for-manufacturing (DFM). Many PCB assembly services companies offer free DFM check services, which you can depend on to lower the printed circuit board assembly cost. To reduce the cost of your bare PCBs, several measures should be carried out in each component.
Layer count. Printed circuit board assembly cost can increase whenever you add more layers. Simply, more layers that you add to one printed circuit board means increasing the PCB assembly expense.
Via tech. Vias, such as blind, buried or micro, have a key function in establishing interconnections on a printed circuit board assembly. In general, adding vias means paying higher costs and smaller diameters, and this makes the PCBs more expensive. So you need to carefully identify the number of vias you only need to lessen the bare PCB costs while guaranteeing adequate functionality.
Size and shape. Printed circuit board assembly should be created neatly and functionally. A board’s size should be based on the specifications of pick-and-place equipment provided by your PCB assembly services partner. This should be done accurately to implement all functions and consider all necessary moderate space. Panels may be required as needed. However, with the changing density and complexities of modern electronics, most small PCBs can be relatively complex. The small size does not necessarily follow low cost. PCB shape also impacts the board’s price. Essentially, standard shapes like square or rectangle have low prices, while specialized shapes are usually more expensive to create.
Surface finish. By avoiding pads from oxidizing, the surface finish assists in ensuring excellent solderability and electric functionality. Various surface finishes (e.g. HASL, OSP, ENIG, ENEPIG, etc.) have both advantages and disadvantages. Always select the surface finish type that is suitable for your printed circuit board assembly’s product’s needs.
In reality, the cost of bare PCBs is determined by multiple factors. Each of them could cause slight fluctuations in the final price. These are only some practical tips on PCB assembly services and assembly requirements.
4.2 Draft an effective and complete bill of materials
The bill of materials (BOM) is a complete list of your raw materials, assemblies, items, sub-assemblies, components, etc. necessary for product printed circuit board assembly manufacturing. Some people might think preparing a BOM is easier than doing the Gerber file. However, more errors tend to be made in the BOM than in the Gerber files.
An accurate listing of BOM should involve essential items for PCB assembly services providers, such as part number, manufacturer’s name, quantity, reference designator, description, case/package, SMT method, top/bottom, points/footprint, and BOM level. Generally, PCBA personnel can use in-house BOM template and create guidelines. You can fill them accordingly to hasten the quotation process.
It’s commonly advised to add a part replacement in your BOM. As electronics continue to change at an ever-increasing pace, course components are upgraded instantly with old parts, at times, can be discarded. Although your PCB assembly services partner can discuss with you about the items that are out of stock, time can be wasted looking for replacements, thus dragging the production process. By providing the complete BOM and replacement, a PCB assembly services partner can provide an accurate quote in a short period and start the production upon your confirmation. It’s always better to anticipate and be fully prepared for any emergency cases.
4.3 The need to adjust order volume and lead time
Order volume is commonly indirectly proportional to every commodity’s price. When your order volume increases, the less expensive it is for each printed circuit board assembly (similar for PCB assembly services). Always consider your organization’s situation and identify your order volumes (such as high, medium or low), then choose a PCB assembly services partner that can easily provide your requested order volume.
Regarding lead time, the main issue lies in the calculation. Don’t be confused by faster lead time of the PCB assembly services provider. Various printed circuit board assembly firms follow different lead time calculations, so ensure to understand the following: When is the start time? When did you order and when is the payment? What day was the arrival of the components? Overall, the rule of thumb on lead time is the longer it is, the lower the price.
4.4 Don’t forget inspection or testing
You might be thinking about the direct relationship between reducing cost and inspecting or testing. Basically, inspection or testing can increase the printed circuit board assembly cost. However, it has been stressed in this article how to reduce cost while maintaining the product quality.
Inspection or testing is vital in ensuring the high quality of the products by eliminating issues, risks or mistakes in advance. However, not all PCB assembly services providers have this service. It’s more efficient to let the products be inspected or tested in the manufacturer’s facility. Under general conditions, a PCB assembly services partner offers reduced cost on inspection compared with those that only deals with the inspection. Also, your products do not need to be delivered everywhere.
Whenever your PCB assembly services provider has inspection service at the final production stage, you should give your test jig to help this testing service implemented well based on your specifications. Common inspection processes include visual inspection to automated optical inspection (AOI) to automated X-ray inspection (AXI).
For huge volume orders, it’s better to do first article inspection on the initial products before the real volume board assembly. It helps to check issues like component orientation and polarity and provide potential modification in a timely manner. If time allows, you can even ask your PCB assembly services partner to provide sample products so you can test them in real circumstances.
Another vital rule is to stick only to one PCB assembly services company as your partner. Working for years with a PCB assembly services provider can help you depend on the company based on its smooth collaboration, mutual credit, and building trust through the years. However, if you’re experiencing difficulties communicating with your PCB assembly services partner or your business is undergoing a cost crisis, then it’s time to do some adjustments.
Strictly following the suggested guidelines cited can help you decide better and select your new PCB assembler. You’ll surely cut down some cost without even sacrificing the product quality.
Chapter 5. How to Choose a PCB Assembly Partner and Metrics Evaluation
Selecting a compatible printed circuit board assembly partner is a challenging endeavor. Good decision-making is vital to achieving the most accurate representation of your prototype to reduce cost and save money.
Many factors have to be considered all the time such as price, lead time, quality control, customization, and minimum order size when searching for the best PCB assembly shop that has the most suitable compatibility for your individual product. When choosing a PCB assembly services partner, the factors below should be highly considered:
5.1 Competency and Capabilities
The expertise of the PCB assembler includes the technical know-how necessary before accepting new projects and can troubleshoot issues before starting the task. The printed circuit board assembler can handle autonomously the project and need minimal input from the customer after the assembly order is ongoing. Validate whether the PCB assembler you are negotiating with has all the certifications required to ensure quality work such as the ISO 9001:2008 standards. The objective of offloading this task to a contract assembler can make things easier and the project to be handled smoothly.
5.1.1 Equipment
Identify the PCB assembler’s list of equipment and know the fabricator’s capabilities to forecast the quality of the end result. The PCB assembler’s capacity to provide a timely order based on the exact specifications depends on the available assembly equipment used. For instance, if the PCB design needs SMT components, then the ideal PCB assembler should have its own pick-and-place equipment, reflow ovens, 3D BGA inspectors, and rework tools. What are the types of equipment that the company uses? If it employs sophisticated machinery, it’s more likely to deliver quality results. Although it’s not always a guarantee that advanced tools mean quality work, in essence, it is a good indicator.
5.1.2 Technical competency and certifications
A quality PCB assembler must have the necessary expertise when accepting projects and must have necessary skills before starting any PCBA project. The printed circuit board assembler must independently with minimal client input once the assembly order is taking place. Verify whether the company has the standard certifications. The purpose of checking this with the contract PCB assembler is to make your life easier. To earn certifications, companies undertake independent reviews by qualified third parties. This should provide you with some assurance that you’ll get a high standard product. ISO 9001:2015 certification, for example, shows that a company follows a recognized quality management system in its work plan and activities.
5.1.3 Industry experience
Printed circuit board assembly is applicable to various industries. A specific industry, for instance, has definite, strict and special requirements regarding manufacturing or processing guidelines. It’s nearly impossible for one PCBA partner to work on all industries available. Basically, each PCBA manufacturer is more proficient in servicing specific industries compared to others. For example, a PCBA house may be well rounded in manufacturing PCBs for smartphones and has the expertise to constrain space in the final products. Those PCB houses focused on space industries are definitely better at doing high-density projects. With this condition in mind, you have to be fully informed of the industries that your PCB assembly partner is good at so are sure that you are dealing with a professional PCB assembly partner instead of a less knowledgeable PCB assembly services provider.
5.2 Customer Services
A good PCBA partner understands the needs of its customers to become a legit partner. The PCB assembler knows how to accomplish the task while providing the highest quality printed circuit board assembly products at the most reasonable prices. It assists in the consultation with the customers in both the ordering and manufacturing processes. The PCB assembly services partner provides its customers’ the best interests when providing innovative solutions to manufacture their PCB products. The PCBA partner provides industry-leading assistance to its customers from placing an order to its final status during manufacturing, especially during delays, upon delivery, and after completion.
5.2.1 Minimum order quantity and lead time
Every PCB project is unique as its size and scope vary based on the specific requirements. One customer may request for a single board for prototyping while another may seek a dozen. A small order for one company can be similar to another. It is highly advised to look for a PCB assembly services company that can provide your order on time based on your specific business needs. For example, PCBA firm specializes in low volume, quick turnover orders. It is best for prototyping new products or smaller production while other printed circuit board assembly firm partners may focus on thousand pieces. Based on the timelines, the lead time is a critical factor. You are advised to scout several PCB assembly companies to identify who among them can provide your order in the shortest time possible. Also, carefully check the project plan and set deadlines. For most PCB assembly services shops, the work starts when after all the necessary parts and boards become available. This is considered as the official “Day 1” of the project.
5.2.2 Customer support and regular communication
Although technical expertise and product quality are essential, customer support is also a vital component. You would want to work with a company that is willing to provide the best solution for you by responding quickly to your queries and willing to fix issues that you encounter.
Getting a glimpse of the quality of a company’s customer service can be achieved by discussing your PCBA project with the representatives from the PCB assembly company that you are dealing with. Identify how they accommodate your concerns and whether they are helpful, knowledgeable and courteous when you talk to them. Identify how quickly they get back to you when you ask some clarifications or concerns. Also, it is very helpful to look for reviews and testimonials online from their previous clients. You might see them on their website, third-party review sites or social media platforms. Be observant how they make an interaction with their clients on social media websites.
Learn more from the PCB assembly services company’s representative about the customer support services they provide. Does the company provide a custom assembly and testing routine activities? If you’re unsure which PCB assembly approach will work best for your project, you might look for this service. If you encounter technical problems with your PCBs, will they be willing to fix them for you? Is the company flexible to provide solutions to meet your target schedule?
The client’s feedback a company gets is a critical indicator of quality work. Check its past works and you’ll know the quality to expect. Search for customer reviews or reach out to existing or past clients and ask them how satisfied they were working with your prospect PCBA partner. Simply by asking, you minimize potential troubles of not doing your research before hiring the company’s services.
5.2.3 Electronic Component sourcing
Make an evaluation of the PCB assembler’s procurement department to identify which vendors offer the best components that will be used in the turn-key service. Ensure the company is sourcing parts from recognized component suppliers and they adhere to the industry standards for overages and counterfeit materials. These experts should be able to provide accurate BOMs based on the design file and the assembler to ensure that the PCB is produced with the exact specifications cited on the BOM. It is also essential to know about their component substitution guidelines in cases where the part you’ve chosen is no longer available. With regard to the service provided by PCB assembler, component sourcing plays a critical part so do your research about its component sourcing expertise such as:
• Good rapport with leading global component providers
• Qualified components procured by them
• Accepting the components provided by customers
• Stocking up surplus components for future projects
5.3 Price and Cost
The proximity of the PCB assembler and the customer’s location is a major consideration when selecting a PCB assembly partner. Overseas assemblers may be cheaper when handling bulk orders, but the delivery time may take a long time of about six months. U.S.-based assembly houses usually have quicker delivery times. Some PCBA shops provide overnight shipping as a standard service. The location is very vital if the design is ITAR or export-controlled. Labor costs differ and are dependent on the assembler’s expertise and the type of service required. Should you be providing the PCB services provider with all the needed parts or save your valuable time by entrusting everything to the assembler to purchase the components? Turnkey assembly minimizes several delays of the PCB assembly process. Customers are only required to submit their design files and the PCB assembly shop will be in-charge to leverage with the part and board suppliers and procure the requested components. However, if you want a hands-on approach, consignment services will allow sending your requested PCB and components by mail and then the project will be done for you.
Chapter 6. Conclusion and How Circuitsify Can Help
Circuitsify is a flexible, customer-focused manufacturing resource for printed circuit board assembly, where we focus on both rigid and flex PCB assembly. Printed circuit board assembly services are performed in a dedicated state-of-the-art, clean room facility and can be combined with our full system integration for efficient, one-stop manufacturing.
Based in Los Angles California and with off-shore manufacturing facilities in “Hardware Silicon Valley”—Shenzhen China, we offer low to medium volume, high mix, PCBA services and end-to-end integration services for products in industries including life-science, pharmaceutical, power management, medical device, semiconductor, and alternative energy. With our exceptional turnkey manufacturing services, Circuitsify is able to produce and fully integrate PCB assemblies for OEMs seeking a one-stop manufacturing solution. By taking fully the advantages of our presence in China, as one of the leading international electronics manufacturing companies we offer competitive price when it comes to pcb assembly in high volumes. Got a project for PCB assembly? please feel free to contact us.
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