Test for Pb or Pb-free?

[Jon Snell]

I think most will agree that the dull lifeless type of solder joint is pretty much a lead free joint as lead keeps its sheen.

The other main issue I had with large scale integrated components, (BGA and 240pin plus large volume ICs) is the 'fingers' that tin 'grows' over time. These do short circuit the pins when very close together.

I remember manufacturing substrates, some years ago for a local plating company, Ti (as they were then) required 3 atoms of gold was to be places upon the legs of the chips to allow good thermal and electrical conduction.
Unfortunately with the electrolysis method used, if the timing was out and they were left in the bath too long, 4 or more atoms of gold got used and that shorted the pins together. What fun we had!

If you think of early X Boxes, when the red light of death apeared, heating the processor up to 185˚C reflowed the 'fingers' back to the leads.
Lead doesn't suffer from the same issues as tin.

[tedmich]

Here is a bit of a retrospective on the "tin whisker" nightmare caused by RoHS lead free requirements:
https://www.theguardian.com/technolo...ch.engineering

The one I remember was the Swatch company supposedly losing $500M worth of watches...they squawked so loud they are now permanently exempt from RoHS requirements for lead free solder!

Here is a good recent review
https://ieeexplore.ieee.org/stamp/st...number=9145523

[Jon Snell]

"Pushing tin

The solution to "whiskering"? Mix lead into the solder, as was done from the 1950s. Colin Hughes, a physicist who worked on the first British nuclear bomb, told me that the whiskering problem never came up during his career."

That is because we didn't have the technology to form leads less than 5thou apart so the problem couldn't arise.

Inreresting though.

[tedmich]

You certainly wouldn't want a visit from the solder police!

well there's definitely more lead in my pencil now, so to speak...

[Mick Bailey]

I remember manufacturing substrates, some years ago for a local plating company, Ti (as they were then) required 3 atoms of gold was to be places upon the legs of the chips to allow good thermal and electrical conduction.
Unfortunately with the electrolysis method used, if the timing was out and they were left in the bath too long, 4 or more atoms of gold got used and that shorted the pins together. What fun we had!

The difference between 3 and 4 atoms of gold is 0.000000144 mm. (5.6693E-9 inches) I can't imagine any chip leg spacing in any application where that difference would result in a short. Plating processes deposit more material on edges and corners than flat areas - how could any local plating company control a deposit to within a single atom of gold?

[Enzo]

We often call ICs "chips", but I think when we are talking gold atoms, the "chip" in question is the actual silicon item INSIDE the ICs. And in there dimensions and clearances are INCREDIBLY tight.