Stencil Aperture Design And Area Ratio The printed circuit board gets the solder paste from a stencil, and the stencil is a sheet of metal with a hole for every pad. The volume of paste that ends up on the pad is set by the geometry of that hole, and…

Copper Surface Roughness and Its Effect on Signal Loss At low frequencies the surface of a copper trace can be rough without consequence, because the current uses the whole cross section of the conductor. As the frequency rises the current crowds into a thin layer at the surface, and that…

Paste in Hole Solder Filling for Through Hole Joints Paste in hole is the technique of printing solder paste into a through hole so that the joint can be formed during the same reflow step that solders the surface mount parts on the board. It removes a wave soldering or…

Board-to-Board and Wire-to-Board Connector Selection Every product has at least one place where two boards or a board and a cable have to connect and still be separable. That interface carries the signal integrity, the mechanical retention and the serviceability of the product, and it is usually chosen from a…

Glass Transition Temperature Effects in PCB Laminates Every laminate datasheet lists a glass transition temperature, and every engineer nods at it without always knowing what it controls. It is not a melting point, and crossing it does not destroy a board. It is the temperature at which the cured resin…

Silkscreen Design Rules for Assembly and Repair Silkscreen is the only part of the board that explains itself to a person. It carries the reference designators, the polarity marks, the connector pin numbering and the warnings, and it is usually the last item to be considered in the layout. What…

Test Point Design for Probe and Fixture Access Test points are the interface between the board and everything that has to prove the board works. They are usually added at the end of the layout, which is why they are often the reason a test fixture is difficult and a…

Solder Mask Sliver and Dam Width Control on Dense Boards Solder mask is not a cosmetic layer. On a dense board it is a structural part of the assembly process, keeping solder where it belongs, protecting copper from the environment and defining the dams that stop a bridge between two…

Failure Analysis: Root Cause and Escape on Assemblies When a unit fails, the first answer is usually a guess. The failure analysis process exists to replace the guess with evidence, and it is only useful if it is followed before the unit is disturbed. Before Anything Is Touched The failed…

Audio Codec Interface Circuit Design An audio codec puts analogue to digital and digital to analogue conversion, a serial audio interface and usually a small mixing and gain stage on a single die. That integration removes a great deal of design work, and it also concentrates the places where digital…