Solder Mask Registration and Print Quality Control Solder mask has to cover the board except where the joints are. Every opening has to be in the right place, every dam between two adjacent pads has to survive assembly, and the surface has to be free of defects that trap flux…

Gold Wire Bonding: Surface Requirements on PCB Pads Wire bonding places a far more demanding requirement on a pad surface than soldering does, because the bond is formed by pressing a fine gold wire against the pad with heat and ultrasonic energy. Any contamination, porosity or thickness variation at that…

Rework Station Thermal Control and Profiles Rework heats a small area of an assembled board, and controlling that heat is harder than controlling a reflow oven because there is no enclosure. The station, the preheater and the operator together decide whether the joint is made and whether anything nearby is…

Assembly Work Instruction Content and Control A work instruction is the document that turns a process into what actually happens on the line. It is written for the operator rather than for the auditor, and the test of a good one is whether a trained person who has not run…

Copper Weight: Preparation, Placement and Process Control Copper spreads heat laterally, and the amount it spreads depends on how thick it is. A design that moves heat away from a component is partly a thermal design and partly a copper weight decision, and the two are usually made in different…

Conformal Coating Rework and Repair Practice A conformal coating protects a board by sealing it, which is exactly what makes repair difficult. Once a unit is coated, any component replacement requires the coating to be removed locally, the repair to be made and the coating to be restored so that…

Moisture Barrier: Design Rules and Process Limits A moisture barrier bag is the last control between a dry part and the humidity of the room, and it only works if the bag, the desiccant, the humidity indicator and the seal are all correct. A bag that is correctly specified and…

Flux Application Methods in Wave and Selective Soldering Flux has to reach the joint in the right quantity and be active at the moment the solder arrives. The application method decides the distribution, the volume and how much of the board is affected. Spray Application A spray produces a fine…

Impedance Coupon Verification for Controlled Boards Impedance coupon verification is the step that proves a controlled impedance stackup is actually being built the way the drawing describes. The board may look correct, the layer count may match and the drill data may be right, yet the trace width, dielectric thickness…

SMT Data Collection and Traceability Records Traceability is the ability to answer a question about a board after it has been built: which paste, which profile, which machine, which operator. The records that answer those questions are worth keeping and the rest are noise. Starting From the Question The useful…