Production Yield Ramp Planning A new product does not start at its mature yield, and the difference between the first week and the tenth is the ramp. Planning the yield ramp means knowing what the expected curve looks like, what will be learned at each stage and what the customer…

Revision and ECN Handling in Production An engineering change is easy to define and difficult to land. The design change is usually the simple part, while the work is in the board revisions in stores, the assemblies already built, the tooling that references the old version and the documentation that…

Shield Can Attachment and Removal A shield can is a metal cover that reduces the electromagnetic field leaving or entering a circuit, and it works only if it is connected to the ground reference at many points. The attachment is therefore electrical as much as mechanical. The can is usually…

Solder Mask Registration and Mask Dam Control The solder mask decides where the solder can go, so its registration is as functional as it is cosmetic. A dam that is too thin breaks down during assembly and a clearance that is too small exposes copper that should have been covered.…

Underfill Application and Flow Behaviour Underfill is a polymer that flows under a package and fills the gap between the solder joints, where it reduces the strain on the balls during thermal cycling. It is applied after reflow and travels by capillary action, which means the process depends on the…

Assembly Material Shelf Life Control Every consumable in an assembly line has a shelf life, and the ones that matter are not always the ones that are tracked. Solder paste is carefully dated, while adhesives, flux, wick, cleaning chemistry and even the desiccant in a bag are often stored until…

Test Fixture Design for Board Assembly A test fixture is a mechanical and electrical interface between the product and the tester, and its design decides how much of the board can be tested and how repeatable the result is. A fixture that is built from the netlist alone usually performs…

Solder Pot Maintenance and Dross Control A wave solder pot is a bath of molten alloy that is used continuously, and both the alloy and the equipment change while it is in service. Maintenance is the discipline that keeps the change inside the limits the process was qualified with. How…

Rework Verdict and Scrap Decision Rules Every rework decision is a comparison between the cost of the repair and the risk that the repair leaves a worse board than the one that was rejected. That comparison is only possible if the condition of the board is known, which is why…

Test Point Placement Rules for Assemblies A test point is a small piece of real estate that decides whether a board can be tested at all. Layout pressure pushes them to the edges and into the gaps, and the result is a board that must be tested with a slow…