Solder Joint Acceptance Criteria: Accept, Reject and Rework Inspection criteria exist so that two people looking at the same joint reach the same conclusion. Where the criteria are not written down, the conclusion depends on who is looking, and the process drifts. What a Good Joint Looks Like A well…

Hand Soldering Quality: Iron Tips, Heat and Technique Hand soldering remains the most versatile soldering method and the least reproducible. The difference between a good operator and a poor one is not dexterity but the understanding of where the heat goes. How Heat Reaches the Joint The iron tip contacts…

Assembly Floor Contamination Control: Sources and Countermeasures Contamination on the assembly floor is rarely dramatic. It arrives on a hand, in a cleaning cloth, from a nearby machining operation, or from an air line, and it accumulates until a batch fails a humidity test for a reason nobody can identify.…

Solder Mask Adhesion: Surface Preparation and Cure Solder mask that lifts, blisters or flakes is almost never caused by the mask itself. It is caused by what was on the copper before the mask was applied, or by the conditions under which it was cured. How the Mask Bonds The…

Watchdog Timer and Brownout Circuit Design An embedded controller can fail in ways that no amount of firmware testing will catch: a supply dip that leaves the core in an undefined state, a clock that starts late, or a code path that stops feeding the watchdog. A supervisor circuit exists…

Hot Bar Soldering: Thermode Choice and Fine Pitch Joints Hot bar soldering joins a row of fine pitch connections in one operation by pressing a heated metal tool onto the joint area, and it is the standard method for attaching a flex tail to a rigid board. The tool transfers…

Tantalum Capacitor Selection: Why Derating Decides A tantalum capacitor packs a large capacitance into a small case, which is why it appears on power rails where a ceramic would need several parts in parallel. It is also less forgiving than a ceramic, and most of the failures attributed to the…

Real Time Clock Circuit Design Guide A real time clock keeps time while the rest of the system is unpowered, which means it spends most of its life running from a small battery and drawing almost nothing. Every microampere matters, every picofarad of load capacitance shifts the frequency, and the…

Solder Balling on SMT Assemblies: Causes and Fixes Solder balling is the small spheres of solder that appear around a joint or scattered across the surface of an assembly after reflow, and it is one of the most common cosmetic findings on an SMT line. The balls are rarely a…

Feeder Maintenance and Tape Handling on the SMT Line A placement machine is only as good as the tape it draws from, and most intermittent placement defects trace back to a feeder that has drifted rather than to the head. Feeder care is unglamorous maintenance with a direct effect on…