Via Plugging vs Tenting: What Solder Mask Should Do to a Via The decision about what solder mask should do to a via is usually made in a single line on the fabrication drawing, and it decides whether the assembly line sees a sealed surface or a row of open…

Fiducial Design and Placement for Vision Alignment A fiducial is the only feature on the board that the placement machine is allowed to interpret, and everything the machine does afterwards is referenced to it. When a mark is undersized, partly covered by mask or placed too close to copper, the…

Reflow Carrier Pallets: Supporting Thin Boards Through the Oven A thin board behaves like a different material once it is hot. The same panel that feels rigid at room temperature loses most of its stiffness above the glass transition and sags between the conveyor rails, so the paste, the component…

Board Handling and Racking Damage Prevention Handling damage is the defect that everyone recognises and almost nobody measures. A nicked board edge, a scratched solder mask, a chipped corner, a bent pin: each is small on its own, and each is attributed to whoever touched the board last. In practice…

Component Floor Life and Moisture Sensitivity Control A moisture sensitivity level rating describes what happens to a plastic package when it absorbs water and is then heated. The absorbed water turns to steam inside the package, and if the pressure is high enough the package cracks, or the internal bond…

Thermocouple Attachment for Reliable PCB Thermal Profiles A thermal profile describes the product, not the oven, and the difference between the two is entirely in how the thermocouple is attached. A bead taped to the solder mask reports the mask temperature, while one bonded to a pad beneath a component…

Press-Fit Connectors: Hole Tolerance and Barrel Plating A press-fit joint is made without solder, and that is precisely why it demands more of the board than a soldered joint does. The connection depends on the hole wall deforming against the pin and staying in contact for the life of the…

Solder Joint Inspection Under Low-Angle Light Solder is a mirror. What an inspector sees on a joint is mostly the reflection of whatever light is aimed at it, which is why the same joint can look perfect under one lamp and defective under another. Low-angle light, directed across the board…

Cleaning Chemistry Compatibility Testing A cleaning process has to remove flux residue without damaging anything else on the board, and the list of things that can be damaged is longer than most process engineers expect. Labels peel, connector housings craze, relay seals take on water, laser markings fade, and a…

Solder Pot: Design Rules and Process Limits A solder pot is a chemical reactor that nobody designed as one. Every board adds copper, every lead adds its plating, and the alloy that started the shift inside specification drifts towards a composition that no longer wets the way the profile assumes.…