PCB Desmear Process Control For Reliable Hole Walls Drilling a multilayer board generates enough heat to soften the resin, and the bit drags that softened material across the freshly cut hole wall. The resulting smear is a thin, electrically insulating film over the inner layer copper, and if it is…

Underfill Application Methods for BGA Solder Joint Life Underfill is a filled epoxy that flows into the gap beneath a package and surrounds every solder joint. It does not make a joint stronger in tension, but it changes how the joint responds to thermal cycling by spreading the strain across…

Solder Ball and Solder Beading Control A solder ball is a small sphere of alloy sitting on the board surface, usually beside a joint and often unconnected to anything. Solder beading is a related but distinct defect in which a ball is attached to the side of a joint or…

Stencil Tension and Frame Selection for Fine Pitch Stencil tension is one of the few stencil properties that changes continuously through the life of the tool, and it changes the printed deposit long before anyone notices a defect. A loose stencil flexes away from the board during separation, which smears…

Router Bit Wear and Depanel Edge Quality Depaneling a panel with a router removes material rather than shearing it, which gives a clean edge and allows almost any outline to be cut. The cut is made by a small carbide bit spinning at high speed while the panel is moved…

Selective Soldering Fixture Design Requirements Selective soldering solders one joint or one group of joints at a time, so the board has to be in the same place for every one of them. That is the fixture job, and it has to do it while the board is heated locally,…

AOI Program Tuning: Cutting False Calls Without Escapes An AOI program is a set of decisions about what an acceptable joint looks like, written as tolerances on measurements the machine can make. The machine does not see a good joint; it sees the area of a fillet, the position of…

Wave Solder Fluxer Setup and Spray Control The fluxer decides how much chemistry reaches the joint before the wave. Too little and the oxides are not removed, so the alloy beads instead of wetting; too much and the board leaves the machine with residue, spatter and a flux that has…

Solder Paste Metal Content And Powder Size Explained Solder paste is an alloy powder suspended in a flux vehicle, and the ratio between the two is the single number that most influences how the paste prints. Suppliers quote that ratio as metal content by weight, which is convenient for them…

Solder Preform: Design Rules and Process Limits A solder preform is a shaped piece of alloy that is placed at the joint and melted in a reflow pass, so the alloy volume is set by the piece rather than by the printing process. That single property is why preforms appear…