Tombstoning And The Forces That Lift A Chip A two terminal chip component can lift onto one end during reflow and stand on its termination like a headstone. The defect is called tombstoning, it happens within a second or two at the moment the solder becomes liquid, and it is…

Design of Experiments for PCB Process Optimisation Process problems rarely have a single cause. Changing one parameter at a time, which is how most process work is done, cannot reveal what happens when two parameters are changed together, and it is inefficient when several parameters need to be explored. Design…

PCB Storage Humidity Control Guide A finished printed circuit board is not inert. The laminate absorbs moisture from the air, the surface finish reacts with the atmosphere, and a board that has been stored badly will fail during the reflow soldering that was supposed to be the easy part. PCB…

Stencil Aperture Design And Paste Release The stencil is the only part of the printing process that decides how much solder paste lands on each pad, and the aperture design is what the stencil maker actually cuts. Every joint on the board, and therefore every solder fillet, void, bridge and…

PCB Dewarping Process Guide A board that has bowed or twisted cannot be assembled reliably. The paste printer cannot hold it flat, the placement machine sees a shifting fiducial and the reflow oven bakes the distortion in. Dewarping is the process that removes the shape after the board has been…

Tdr Impedance Measurement: Design Rules and Process Limits A TDR impedance measurement sends a fast edge down a trace and watches the reflection that comes back. The reflection is a picture of the impedance along the line, so the instrument shows the trace, the via, the connector and the pad…

Second Source Qualification for Electronic Components Supply problems, lead times and end of life notices all push manufacturers to qualify a second source for a component. The temptation is to treat it as a paperwork exercise and approve an equivalent part number. The reality is that two parts with the…

Insertion Loss Budget Guide An insertion loss budget is a list of every loss in a high speed channel, added up before the layout begins. The driver, the package, the board, the vias, the connectors and the cable all contribute, and the total has to leave enough signal at the…

Copper Foil Roughness: Design Rules and Process Limits Copper foil roughness is easy to ignore because the foil itself does not look rough. The side that faces the laminate is treated to give the resin something to grip, and the treatment is a surface profile measured in microns. At low…

Four Wire Kelvin Measurement of PCB Trace Resistance Measuring the resistance of a copper trace looks straightforward until the number matters. A trace a few centimetres long may have a resistance of a few milliohms, and the probe contact resistance in a two wire measurement can be larger than the…