SMT Female Headers: Coplanarity, Locating Pegs and Reflow

The failure mode is a floating row

A long insulator with a row of leads will wet at the ends first if coplanarity is poor. ICT then sees a few high-resistance pins. Extra solder paste rarely fixes a coplanarity problem.

Design and incoming quality

• Specify coplanarity (often around 0.10mm, series-dependent) and inspect it; cosmetics are not enough.
• Locating pegs need correctly placed holes; a shifted hole drags leads off the pads.
• Pads slightly longer than the lead help self-alignment; solder mask must not lift one end.
• For long dual-row parts, stencil experiments (slightly larger end apertures) should be run with process engineering.

Plastic vs profile

Lead-free reflow needs PA6T or LCP, not commodity nylon. Respect MSL baking, especially in humid seasons, to avoid blistering on a second reflow.

Junjia SMT female headers can be supplied on tape. For NPI, check solder at the lead heel after reflow, not only whether the housing looks centered.