Component Orientation and Polarity Checks A reversed component is a defect that the electrical test will find and that the functional test may not, depending on the circuit. Detection during assembly is far cheaper, and it depends on the design providing the information the process needs. The polarity check is…

Solder Balling in Reflow and How to Stop It Small spheres of alloy scattered around a joint are one of the most common cosmetic defects in reflow assembly, and one of the most misleading. Solder balling is usually reported as a paste problem, but the cause is often in the…

Copper Thickness Verification: X-Ray and Microsection Copper thickness is one of the few characteristics of a printed board that is specified numerically on every drawing and verified on every order. It sets the current carrying capacity of a trace, the impedance of a controlled line, the thermal performance of a…

Solder Defect Pareto and Prioritisation A defect pareto ranks the causes of defects by their frequency, and its value is that it shows where the effort should go first. The measurement is simple and the discipline is in acting on the result before moving to the next problem. The pareto…

Standard Work for Line Changeover A changeover is a period during which the line produces nothing, and its length determines how small a batch can be run economically. Standard work for the changeover is what makes the duration repeatable, which is what allows a schedule to be planned. The work…

Solder Pot: Design Rules and Process Limits The solder pot is the one component in a wave soldering line whose composition changes every hour it runs. Alloy is consumed through the joints, oxides are skimmed off the surface, and metals dissolve from boards, finishes and fixtures into the bath. Level,…

Solder Mask Adhesion, Wicking and Cure Control Solder mask is a permanent coating rather than a paint, and it has to do three jobs at once: protect the copper, define the areas that will be soldered, and survive assembly. Adhesion and wicking are the two ways it fails, and both…

EMI Gasket and Contact Design A gasket is the part that closes the gap between a shield and a housing, and it works only if it is compressed and if the contact surfaces are conductive. The design is therefore about force and about surface, not about the gasket material alone.…

PCB Handling After Conformal Coating A coated assembly is more robust and also more difficult to handle, because the coating can be damaged and because the film continues to change after it is applied. The rules for handling, curing and rework therefore differ from those for an uncoated board. The…

Work Instruction and Visual Aids A work instruction is the document that tells an operator what to do at a station, and it is read more often than any other document in the factory. Its quality therefore has a disproportionate effect on consistency. The instruction should be written for the…