Laser Soldering: Spot Size and Heat Input Control Laser soldering delivers energy to a joint as a focused beam rather than by conduction from a hot tip. The heat is absorbed at the surface where the beam lands, and it spreads into the joint by conduction from there. That makes…

Tin Whisker Inspection and Mitigation in PCB Finishes A tin whisker is a thin, single-crystal filament of tin that grows out of a tin-plated surface without any applied voltage. Whiskers are typically a few micrometres in diameter and can reach several hundred micrometres in length, which is enough to bridge…

Electropolished Stencil Apertures: Paste Release and Surface Finish An electropolished stencil has had a thin layer of metal removed from the walls of its apertures by an electrochemical process, which smooths the surface left by laser cutting. The change is measured in fractions of a micrometre, but it acts on…

Entry Burr Control in PCB Drilling: Causes and Removal An entry burr is the ring of copper pushed up around the rim of a hole where the drill enters the board. It forms because the drill lifts the copper foil as it cuts through, and the material has nowhere to…

Voids in Through-Hole Solder Joints: Where the Gas Comes From Voiding in through-hole solder joints is the formation of gas pockets inside the solder that fills a plated barrel. The joint can pass a visual inspection and still carry voids that reduce its cross section, and the barrel fill measurement…

SMD Adhesive Dispensing Before Wave Soldering On a mixed technology assembly, the chip components on the underside are held in place by dots of adhesive before the board crosses the wave during wave soldering, where the contact geometry is covered in the notes on wave height and contact. The adhesive…

Drill Bit Point Angle and Web Thickness: What the Hole Sees The point of a printed circuit drill bit is a cutting tool with a geometry that is chosen for the laminate, the hole size and the machine. The point angle, the web thickness, the relief and the surface treatment…

Choosing Test Methods From IPC-TM-650 for PCB Quality Control Most of the numbers that appear on a printed circuit specification, from peel strength to moisture absorption, are produced by a named test method. The method fixes the coupon, the conditioning, the sample size and the way the result is calculated,…

Reading IPC-4761: Via Protection Types and What They Deliver Via protection is one of the few areas where a single number on a fabrication drawing commits the supplier to a specific process. The classification system in IPC-4761 describes seven ways of protecting a via, from a solder mask tent over…

Glob Top Encapsulation: Dispensing and Cure Control A glob top is a dome of filled epoxy dispensed over a bare die or a delicate area of an assembly to protect it from moisture, contamination and mechanical damage. It is the cheapest encapsulation available for a chip on board product, and…