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…
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…
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…
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…
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…
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…
Laminate Selection for High Temperature Boards Laminate selection is usually settled by price and availability until a product fails a thermal test, and then it becomes the most discussed decision on the board. The properties that matter are the ones that describe how the material behaves when it is hot,…
No Clean Flux Residue Risk on Assemblies A no clean flux is not a flux that leaves nothing behind; it is a flux whose residue has been qualified as safe for the product it is used on. That qualification depends on the environment, the voltage and the humidity, so a…
Print Stroke Speed and Stencil Separation Control in SMT Solder paste printing is a filling and releasing operation, and both halves of it are governed by speed. The squeegee has to push paste into the apertures quickly enough to be productive but slowly enough for the paste to fill them,…
Impedance Test Coupon Design And Verification A controlled impedance requirement is a promise about a transmission line, and the only way to know whether the promise was kept is to measure a line that was built with the same process as the product. That is what an impedance test coupon…
