Panel Array Yield Analysis in SMT Production Yield data is generated at every station, and most of it is thrown away. A defect that is recorded only as a number tells the process engineer that something happened, while a defect recorded with its position on the panel tells them where…

Thermal Relief Design In Copper Planes A pad that is connected directly to a large area of copper is difficult to solder, because the copper conducts heat away from the joint as fast as the iron or the oven supplies it. The usual answer is a thermal relief: a pad…

Selective Soldering Design Guide Selective soldering solders one joint at a time with a small fountain of molten alloy. It exists because a modern board mixes fine pitch surface mount parts with a handful of through hole connectors, and the wave process that would once have soldered those connectors would…

Wave Solder: Preparation, Placement and Process Control Wave solder is the process that solders a whole board in a few seconds by dragging it across a standing wave of molten alloy. The board design has a larger effect on the result than most engineers expect, because the solder has to…

BGA Solder Void Causes And Their Control A solder void is a bubble of gas trapped inside a joint. In a ball grid array joint it appears on an X-ray image as a dark circle inside the bright disc of the ball, and it is one of the most frequently…

Stencil Cleaning and Storage Practice A stencil is a precision tool that is treated as a consumable, and the tension between those two facts is what makes cleaning and storage worth a procedure. The same foil that prints a fine pitch pattern cleanly will produce bridging if a single aperture…

SMT Nozzle Cleaning and Placement Reliability Control A placement nozzle picks a component up with vacuum, carries it at high speed and puts it down within a fraction of a millimetre of where the program says it should be. Anything that reduces the vacuum, changes the tip geometry or leaves…

Head in Pillow and Solder Ball Joint Defects A head in pillow defect is a joint where the ball and the paste have both melted but have not united. The ball keeps its spherical shape, the paste has formed a fillet below it, and the two meet along a boundary…

Reflow Profile Design Guide A reflow profile is the temperature history that a board experiences as it passes through the soldering oven. The profile has to melt the solder at every joint, activate the flux without burning it, and complete the alloy without cooking the components. It is a curve…

Heavy Copper PCB Plating And Trace Thickness Most boards are built with one ounce of copper on each layer, which is about 35 microns after plating. Boards that carry motor current, battery current or the output of a power supply need more, and the term heavy copper covers the range…