PCB Fabrication Assembly From Mechanical Damage
PCBs are delicate, thin pieces that can suffer mechanical damage during production. Impacts, abrasion, bending stresses, and contact with fixtures inflict these damages. Careful handling procedures and protective storage racks minimize them. But even the best precautions can’t eliminate all mechanical defects. Understanding the most common causes of these defects allows preventive measures to be implemented.
Most PCBs have a substrate of fiberglass or another material that provides a strong foundation and helps resist breakage. Then comes a layer of copper that may be foil or a full-on coating. The purpose of the copper is to carry electrical signals from one side of the board to the other, just like your nervous system carries signals between your brain and your muscles.
The next layer is solder mask, which shields the copper from contaminants and ensures that soldering paste adheres properly to component pads. This is crucial to the operation of your circuit boards, as incorrect soldering can lead to shorts and other issues that affect reliability.
Depending on the type of PCB, you’ll also have a plated through-hole (PTH) or surface-mount technology (SMT). A PTH is a hole drilled all the way through the PCB that enables a connection with wires or other components. A SMT is a small bump on the surface of the PCB that accepts a chip or other component, similar to how an automaker puts a bolt in a wheel.
When designing a new PCB, it’s important to follow the design guidelines that are set by your contract manufacturer. These will help you create a good design that’s suitable for assembly and can withstand expected voltage, current, and environmental factors. This design verification process is called “design for manufacturability” and is an important part of the entire pcb fabrication assembly process.
Protecting PCB Fabrication Assembly From Mechanical Damage
Most dimensional defects in PCBs are caused by contamination during the manufacturing process. Flux residues, finger oils, metal particles, chemical solutions such as etchants and plating baths, dust and debris all contaminate PCB surfaces and cause shorts, corrosion, and other problems that impair assembly and operational reliability. Thorough cleaning between each wet process step and keeping production areas clean reduces contamination risks.
Another source of dimensional defects is improper sizing of components or incorrect layouts. For example, if the solder bridges that form between pads of fine pitch components are too wide, they can cause shorts and other damage. This is a common problem that can be prevented by careful design and layout review.
Once the tin has dried, it is removed and the bare copper is exposed. The conductive areas of the plate are then plated with tin. The tin is then chemically stripped to expose the copper in precise areas that will form the conductive paths, pads and other patterns on the finished PCB.
It should have a minimum bend radius of 0.1mm and incorporate thermal mitigation features, such as cover layers, to protect the conductive traces from oxidation. It should also have appropriate trace widths and spacing to facilitate reliable electrical connections, and it should use stiffeners in areas that must maintain a specific shape or where connectors are attached.