PCB Assembly

Custom PCBA: Advantages & Key Steps Explained

How exactly do printed circuit boards fit seamlessly inside electric vehicles, cameras, medical devices, and other electronic devices that we encounter on a day-to-day basis? The printed circuit boards that hold together the electronic components are designed, fabricated, and assembled to suit their applications. These circuit boards can come in different dimensions, shapes, and sizes, where designs and functionalities can be tweaked according to end-user applications. This modification according to customer needs and preferences is more popularly known as Customization.

What is Custom PCBA?

Custom PCBA is short for customized printed circuit board assembly. It means assembling circuit boards according to customers’ own design of Gerber and BOM files. Custom PCBA (Printed Circuit Board Assembly) accommodates flexibility in the design to come up with a final product that is tailored to customer specifications while taking into consideration cost, quality, functionality, and reliability. What are the different custom PCBA processes?

The Advantages of Custom PCBA

What are the advantages of custom PCBA? Below is the list of custom PCBA advantages that make it the best option in the electronics manufacturing industry.

Custom circuit board assembly

Cost Viability

Custom PCBA makes possible modifications in the use of different types of materials, design iterations, and processes in favor of cheaper cost and assembly price.

Design Flexibility

With custom PCBA, the design can be adjusted to meet the specifications having the desired device performance, material combinations and geometric configuration. For example, custom circuit board assembly is not restricted to rigid type only and can potentially support other laminate types like flexible polyimide and rigid FR4 substrates.

Performance and Reliability

As earlier discussed, custom circuit board assembly undergoes design and prototyping to evaluate the performance of the design. During this stage, design for manufacturing (DFM) is also conducted to comply with the design rules and requirements to have consistent manufacturing output. Some software can already automatically feedback assessments on the design.

Lastly, and the most important question: how do look for a reliable custom PCBA supplier? Supplier selection is a decision that cannot be made without systematic assessment. At the minimum, the below factors must be weighed accordingly to measure a supplier’s potential as a custom PCBA supplier.

Cost

This factor cannot be overstated enough. The right custom PCBA supplier should be able to provide reasonable quotations for the materials, assembly, and tooling price. At the beginning stage, cost is the quickest indicator if the supplier can be further assessed to the next level.

Quality

Although the provided cost is high, if the quality controls are not sufficient, the supplier is not a good candidate as a custom PCBA partner. The supplier must be able to provide evidence that they will be able to process the parts correctly and consistently. The suppliers must provide proof of certification from internationally recognized companies like IPC and UL to justify that they are compliant with standards.

Delivery Leadtime

A significant factor in choosing a reliable supplier is its ability to provide the parts at a short lead time. Note that PCBA is just part of a bigger supply chain so it is important that the parts will be shipped at the agreed time, with the committed delivery volume.

Capability

A right custom PCBA supplier must have an assembly line with machines that are able to process the parts according to specifications. For instance, if the PCB design has very limited width spacings and the boards are subjected to a component placement machine without the capability to handle intricate board designs, the result may be gross failures. Therefore, the tolerances of the machines, processing and detection capability must all be discussed with the supplier.

 

Key Steps in Custom PCBA

There are many steps involved in custom PCBA, such as PCB design, solder paste printing, components placement and insertion, components soldering, quality inspections and tests. Custom PCBA consists of the following major steps from inception to the final PCBA product. Usually both SMT assembly and THT assembly will be used in custom PCBA.

SMT was developed later than the more conventional way of processing which is called Through Hole Technology (THT). THT is also the placement of components but rather requires bigger spacings since the parts are inserted through the holes and soldered on the other side of the boards. SMT makes possible mounting of components with very narrow spacing. Custom PCBA also means being able to assemble through a combination of SMT and THT processes.

Custom PCBA

Design and Prototyping

Custom PCBA starts with the conceived idea of its requirements and specifications. The design of the printed circuit boards must first be evaluated and finalized. The design output usually consists of a Gerber file format which is an industry-known type of design file. PCB designers should also focus on material properties and mechanical behaviors especially when subjected to thermal and mechanical stresses. Wrong choices of components and materials may entail yield and reliability issues. There are industry standards that have to be followed like IPC-2221.

Stencil Printing

The assembly proper starts by applying the solder paste on the PCBs at specified locations according to the design layout. The application of the paste is done by using a stencil and a squeegee to evenly spread the paste into the apertures of the stencil. Process controls during stencil printing must be considered such as solder paste volume, alignment, and right viscosity of the paste. Due to the regulations on hazardous wastes, solder paste material has been changed from lead-based to lead-free composition such as SAC305 which is made of tin, silver, and copper. But this step is not needed for PTH assembly.

Component Placement

The components are then picked and placed into the printed circuit boards according to the solder paste locations. Custom PCB assembly allows the placement of components of a wide range of sizes and types. Component placement machines have certain tolerances and capabilities based on the minimum size of chips that can be mounted and placement speed. The goal in component place is to have as many printed circuit boards in one panel to increase throughput and cost-effectiveness. In PTH assembly, components can be inserted in the PCB holes manually or automatically by machines.

Reflowing Soldering and Wave Soldering

The printed circuit boards go through a reflow process to melt the paste and achieve a fully cured solder joint. Custom PCBA needs an optimum thermal profile following these steps: pre-heating, ramp up, soaking at peak temperature and cooling processes.  Temperatures and durations must all be evaluated to achieve a quality solder. The reflow oven consists of controllable heating zones with an N2 inert environment to ensure good adhesion of the solder paste to the contact pads of the PCBs.

Wave soldering is used in PTH component assembly. When the components are all inserted and inspected, the PCB boards will run through a wave soldering machine with boiling tin in it. And the pins will be soldered on the PCB when come out.

Automated Optical Inspection (AOI)

Automated optical inspection or AOI machine serves as a quality verification step through image processing software and high-speed cameras. With the increasing complexity of custom PCB assembly, the right lighting, resolution and depth of field are very important imaging parameters that must be optimized so that even the smallest components and intricate parts of the PCBs can be inspected properly. False calls are the main concerns for AOI especially wrong acceptance of faulty PCBs that may lead to escapees. This is further mitigated through subsequent testing processes.

Conclusion

The applications of electronics are boundless. More and more manufacturers and assembly contractors have kept pace with the increasing demand for electronics. Custom PCBA enables functionalities that cannot be done through standard methods. Custom PCBA is defined through the progressive knowledge in electronics technology. Ten years from now, the world we live in will have more intelligent, portable devices and amazing breakthroughs to solve inefficiencies and increase conveniences.

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