Board Edge Clearance Rules for Assembly A board edge is a boundary with several requirements attached to it. Components must stay back from the edge for handling, copper must stay back for routing and plating, and fiducials and tooling features must sit within defined zones. These rules are usually expressed…

Thermal Profiling of Large Assemblies A large assembly does not heat evenly, and no single thermocouple can describe it. The profile that governs the result is the one at the coldest joint and at the hottest joint, and the process has to satisfy both at the same time. Profiling a…

Thermal Pad Soldering with Solder Preforms A thermal pad carries heat as well as current, and both depend on the joint beneath it having a large contact area and few voids. The joint is larger than any other on the board, which is why it is handled differently. Why the…

Footprint Design for Reflow Soldering A footprint is the interface between the component and the process, and it determines how much paste is needed, where the joint forms and how much force the stencil applies. Getting it right removes a whole class of defects before they appear. The dimensions on…

Component Polarity and Rotation Errors in SMT Assembly A polarity error puts a polarised component in backwards, and a rotation error puts it at the wrong angle. Both pass a placement check because the part is in the right position with the right shape, and both may pass a functional…

Counterfeit Component Inspection Methods for Assembly A counterfeit component is not always a fake part. It can be a rejected part that has been re marked, a lower grade part that has been sold as a higher one, a used part that has been cleaned and re taped, or a…

SMT Scheduling and MRP Data Accuracy Scheduling an assembly line is a data problem before it is a planning problem. The plan is only as good as the setup times, the machine rates and the material availability recorded in the system, and those records are usually stale. When the data…

Decoupling Capacitor Placement and Via Design A decoupling capacitor does one job: it supplies charge to a device faster than the power supply can respond. Whether it succeeds depends far more on the loop between the capacitor and the device than on the capacitance value printed on the part. The…

SMT Process Audit Checklist An audit finds the gap between the documented process and the one that is actually running, and on a mature line those two are never identical. The value of the audit is in closing the gap while the knowledge of why it opened is still available.…

Solder Paste Storage and Thaw Practice Solder paste is a chemically active material with a shelf life, a floor life and a working life, and each of them ends for a different reason. Treating the three as one rule produces either waste or defects, depending on which way the assumption…