Reflow Atmosphere Oxygen Level Control Reflowing in nitrogen reduces the oxygen around the joint, which reduces the oxidation of the alloy and the pad during the melting phase. The result is better wetting, a wider process window and, in some cases, a lower defect rate. The oxygen level required depends…

PCB Cleanroom Risks: What Could Go Wrong Electronics manufacturing has become a discipline of small details. Solder paste volumes, placement accuracy, temperature profiles and inspection limits all add up to the final result. This guide looks at PCB cleanroom risks from the perspective of a PCBA factory floor, covering managing…

Warpage Measurement: Design Rules and Process Limits Warpage is measured as a deviation from a reference plane, and the reference plane is the part of the measurement that is most often left undefined. Two inspectors measuring the same board with different supports will report different numbers, and both will be…

PCB Cleanroom Review: A Second Look Electronics manufacturing has become a discipline of small details. Solder paste volumes, placement accuracy, temperature profiles and inspection limits all add up to the final result. This guide looks at PCB cleanroom review from the perspective of a PCBA factory floor, covering reviewing cleanroom…

Wash Bath: Cleaning Bath Monitoring and Contamination Control A cleaning bath is a chemical process that changes as it is used. Flux dissolves into it, the active chemistry is consumed, the rinse water concentrates and particles accumulate. The bath that cleaned perfectly on Monday may be leaving residue by Friday,…

Functional Test Fixture Design and Upkeep A functional test fixture holds the assembly, connects it to the test equipment, and lets the test programme exercise the product the way it will be used. It is a piece of equipment in its own right, with an alignment tolerance, a wear life…

Design for Test Coverage Analysis Test coverage is the proportion of the possible defects on a board that a set of tests can actually detect. It is not the same as the number of tests, and it is not the same as the yield. A board with a hundred test…

Solder Joint Volume and Pad Geometry Solder joint volume is one of the few characteristics of an assembly that is decided at the design stage and then reproduced, or not, by the process. The land pattern sets how much solder the joint can hold, the paste deposit sets how much…

Voiding: Preparation, Placement and Process Control Voids under a QFN thermal pad are the most common measured defect on modern assemblies, and they are also the one most often reported without context, because the number depends on how it was measured. The mechanism is straightforward and the corrections are known,…

Tip Temperature: Design Rules and Process Limits A soldering iron has a setpoint on its display and a temperature at its tip, and the two are not the same. The display reads a thermocouple inside the heater or the tip, and what the joint experiences is the temperature of the…