Industrial Control 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.

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.