Double Sided Reflow Support and Process Control A double sided assembly is reflowed twice, and the second pass runs with components already attached to the underside. Those components are held only by their solder joints, which are molten again during the second pass, or by an adhesive that has to…

Carrier Tape and Reel Packaging Standards A component is only useful on a production line if the machine can find it, pick it and place it reliably, and that depends entirely on the packaging. Carrier tape and reels are standardised precisely so that equipment from different makers can handle parts…

Fusing Current: Design Rules and Process Limits A copper trace is a fuse that nobody specified. It has a resistance, it heats when current flows, and above some current it will open. Most of the time that behaviour is undesirable, but there are cases where the trace is deliberately relied…

Solder Joint Fatigue Life Estimation A solder joint in a product that cycles between temperatures will eventually fail, and the engineering question is when. Estimating that life is what allows a design to be accepted for a ten year service period without waiting ten years to find out. The methods…

Brittle Fracture in Lead Free Solder Joints A brittle fracture in a solder joint is a separation that happens without the deformation a ductile failure would show. The fracture surface is flat and granular rather than torn, and the failure occurs at a load lower than the joint would normally…

Copper Pour Versus Hatched Pour on Inner Layer Planes Every inner layer needs some copper left behind after etching, and the question is whether that copper should be a solid plane or a grid. The choice affects impedance, thermal behaviour, laminate stress and how easily the board can be built.…

Low Temperature Solder Alloys and Their Behaviour A low temperature solder alloy melts well below the standard lead free range, which allows an assembly to be reflowed at a temperature that the components and the laminate can tolerate more easily. The benefit is real and the trade offs are equally…

Bow and Twist Measurement in PCB Panels Bow and twist are the two ways a panel loses its flatness, and they are measured differently, caused differently and corrected differently. They are grouped together in most specifications, which is a source of confusion when a lot is rejected and nobody is…

Silkscreen Legibility Rules for Densely Packed Boards Silkscreen is the part of a board that people read when something has gone wrong. A technician repairing a dense assembly needs to find R47 among a hundred passives, and the legend is what makes that possible. On tightly packed boards every millimetre…

Kit Verification and BOM Accuracy A kit is the collection of material for one build, gathered before the build starts and verified against the bill of materials. Done well, it moves the verification away from the machine, where every mistake costs production time, to a bench where a discrepancy can…