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Common PCB Assembly Faults and How to Prevent Them

One of our main goals at Bittele Electronics is to take steps to minimize and prevent all common assembly faults before they have a chance to appear on your boards. This is one of the many ways that we ensure the highest quality possible for your projects. Due to the varying complexity for each printed circuit board design, we understand that there are many opportunities for PCB failure issues to arise if proper care is not taken beforehand. We understand the manufacturing process and using our knowledge and consideration, we take a variety of steps in order to prevent these issues. Many of these common issues are listed in the following paragraphs.

Design for Manufacturability (DFM) checks.

Bittele Electronics offers Free Design for Manufacturability (DFM) checks in order to help reduce the risk of common PCB assembly faults occurring. Its purpose is to assist our customers in the design phase of their circuit boards so that they can be manufactured quickly and efficiently. Our DFM guidelines define the various tolerances, rules, and testing procedures to which Bittele Electronics adheres during PCB manufacturing.

X-Ray inspection.

Bittele Electronics preforms X-Ray inspection of leadless parts such as BGA components, to ensure that proper solderability is attained. For more information, please refer here.

Via in pad.

Consider, if in your design there are vias on or touching certain pads, also known as “active pads”. When a via is designed within an SMT pad, there is a high risk of solder leakage through the pads during assembly. In order to combat this, a non-conductive epoxy is generally used, however, this comes at a cost. If the vias are small enough and few enough, it may be possible to just fill the holes with solder mask with no risk to your boards.

Solder bridges.

A short may occur during assembly if there is an insufficient solder mask between pins. Designing boards without properly distributing the weight of the components can also contribute to this. It is very important to design the pads to have enough space between them and the solder mask layer. Component alignment issues may also occur if a proper X-Y file is not implemented, as it is very important to the SMT assembly. For a detailed example on how to generate pick and place files on Eagle, Altium and ORCAD/ALLEGRO, please refer here.

Clearances.

Insufficient copper to edge clearance, where traces too close to the edge of the board can cause damage to occur during routing. If the copper is too close to the edges, during trimming, part of the coating that protects the copper from corrosion and interacting with the environment can be trimmed as well. If this occurs the copper would then be exposed, and it would be possible for exposed copper planes to make contact with one another by touching a conductive metal at the same time (which would of course cause a short). A bystander will also have an increased possibility of receiving an electric shock. For this reason, it is very important that the minimum clearances for the specific type of board that is being fabricated are adhered to.

Plating voids.

Insufficient copper plating on the inside walls of holes on the PCB. The can cause the boards to be defective as the electrical current will not be able to pass between the layers. We can avoid this by ensuring that the holes are thoroughly and properly cleaned after drilling. This helps to prevent any contamination of the material or air bubbles inside of it.

De- wetting/Non-wetting.

De-wetting can occur when the molten solder does cover a lead or pad, but then retreats and leaves behind a mound of solder. Non-wetting occurs when the solder only partially covers a surface, leaving some exposed copper behind. Both of these issues can be avoided by making sure the component parts are still within their usable shelf lives and the flux being used must not be past it’s prime (after long hours of use).

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