Thermal Interface Material and Heat Sink Assembly A heat sink is only as good as the joint between it and the device. Two nominally flat surfaces touch at a small number of high points, and the air in the gaps between them is a poor conductor. The thermal interface material…

Feeder Setup, Tape and Reel Verification The feeder is where the component enters the process, and its setup decides whether the placement program sees the part where it expects it. Most “placement” defects are feeder defects. What the Feeder Does The feeder advances the tape by one pocket each time…

Back Drilling For Stub Removal In High Speed Boards A plated through hole that connects an inner layer to the surface continues all the way to the opposite side of the board, because the hole is drilled through the whole stack. The portion of the barrel below the layer that…

Alloy: Key Checks Before Release Alloys marketed for the same purpose differ in their fatigue behaviour, their melting range and their cost. The choice is usually made on melting point and price, and the property that decides the life of the assembly is usually not considered. What the Alloy Has…

Fabrication Drawing Notes That Prevent Substitution An engineering drawing is a communication, and most of the cost it creates comes from what it does not say. A note that leaves a value to the shop is a value that will be chosen for the shop rather than for the design.…

Flicker Free LED Driver Design Flicker in a light source is measured by how much the light output changes and how often, and the eye is far more sensitive to it than most designers expect. A driver that passes an electrical specification can still produce a light that causes headaches,…

Electrochemical Migration Testing and Prevention Methods Two conductors a fraction of a millimetre apart, a thin film of moisture, a little ionic residue and a voltage difference. That is all it takes for metal to dissolve from one conductor and grow back as a filament reaching toward the other. Electrochemical…

Conformal Coating Coverage, Thickness and Cure A board that works on a bench and fails in the field after a few months of humidity is usually the victim of an electrochemical process rather than a defective component. The damage is slow, invisible at first, and driven by the combination of…

Solder Mask Thickness And Its Effects On Assembly Solder mask is a liquid that is printed, dried, exposed, developed, and cured, and the film that results is thinner over a bare laminate than over a trace and thinner at the edge of a feature than in the middle. The nominal…

Process Control for Prototype and Low Volume Assembly Small volumes and prototypes are built with the same processes as production and without the process control that volume pays for. The result is a first article that is not representative of what will follow. What Is Different at Low Volume At…