Solder Preform Application in Power Assemblies A solder preform is a shaped piece of solder placed in the joint before heating, and it is used where paste cannot deliver the volume the joint needs. Power assemblies, thick metal tabs and large thermal pads are the usual places, because those joints…

Solder Preforms in High-Power Assemblies Solder paste is a convenient way to deliver alloy, but it is mostly flux by volume once the volatile fraction has boiled away. On a heavy copper joint the paste can supply far less metal than the joint needs, and the voiding that results is…

PCB Assembly Cost Model and Drivers Assembly cost is driven by the number of placements, the number of process steps, the test method and the rework rate, and it is usually dominated by the first two. Understanding the model allows a design to be assessed before it is built. The…

Press Cycle Design for Multilayer PCB Lamination: A Guide The press cycle is the thermal and pressure recipe that turns a stack of inner layers and prepreg into a bonded multilayer board, and it is one of the few steps in fabrication where a single mistake destroys the whole panel…

Drill Bit Wear and Hole Quality Management A drill bit wears with every hole it makes, and the wear shows up in the hole before it shows up on any inspection report. Diameter, wall roughness, burr height and registration all move as the cutting edge dulls, and the shop has…

Rework Site Preparation and Pad Repair Rework begins with the site, not with the component. A site that still carries the old solder, the old flux and the heat history of the previous assembly will not produce a joint as good as the original, whatever tool is used. Removing the…

Test Fixture Design and Probe Selection An in circuit test fixture holds the board and brings a set of spring loaded probes into contact with the test pads. Everything it measures depends on those contacts being reliable, and the contact depends on the probe and the pad being designed for…

Surface Energy: Surface Preparation Before Conformal Coating A coating adheres because it wets the surface and then cures in contact with it. Where the surface energy is too low or a contamination layer sits on it, the coating sits on top instead of bonding, and the failure appears at a…

Solder Paste Volume Measurement with SPI Paste volume measurement turns the printer into a measurable process. Instead of judging a deposit by its appearance, the system reports a number for every aperture, which can be compared with a target and tracked over time. The value is in the feedback rather…

Incoming Inspection for Components Incoming inspection exists to catch the problems that the supplier’s own checks did not, and to create a record that a later failure can be traced to. It is not a substitute for supplier qualification, and it should not be sized as though it were. The…