Archive for February 7th, 2009
Speaking of things that don’t work, these header pins from my stash have developed some sort of rot. They’re genuine Brand Name pins, albeit a few decades old, and have been stored in the original bag in various basements along the way.
What’s supposed to happen: you touch a pin with a soldering iron and some solder, the solder melts and wets the pin. If the pin is in a circuit board at the time, the solder bonds it to the pad surrounding the hole. Nothing exciting here, except that when I tried to use these pin headers, that didn’t happen.
The symptom is that the headers are unsolderable: the solder doesn’t wet the pins.
The detail view shows what does go on. When I touch a the pin, the original solder plating scoots out of the way, exposing the underlying metal (or whatever it is). Neither tin-lead nor tin-silver solder wets the surface, so the pin can’t be soldered.
The flux forms a layer over the new surface and doesn’t do its usual job of cleaning the metal. Scraping the pin clean doesn’t seem to help, either. In fact, nothing helps: that whole bag of headers is a dead loss.
I’m sure these things worked when they were fresh, but that was a long time ago. I’m not sure what sort of change could occur underneath the original solder plating.
So I picked up some new headers with what passes for gold plating these days and they work fine.
The pix come from my pocket camera on the binocular microscope, using my homebrew adapter.