Q: Gold colored coating on surface mount contacts

[Paul Andrews]

What is the gold/amber colored coating on the contacts of this chip? The contacts aren't gold, and when it is reflowed it just bubbles up as gunk.

[Bill Notfaded]

Did you figure it out Paul? Now you have me wondering too...

Bill

[Paul Andrews]

No. Still don’t know what it is.

> On Aug 19, 2019, at 11:01 PM, Bill Notfaded <notf...@gmail.com> wrote:
>
> Did you figure it out Paul? Now you have me wondering too...
>
> Bill
>

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[johnk]

When "we" were manufacturing in the '90s the safe storage time for SMD was around 3 to 6 mths. Surfaces weren't 'fresh' after that. Some was wave soldered some reflow.
If that is a slow moving component then maybe they coated it with a solder-thru protective layer? Doesn't seem like they used a low activity flux coating from that description.
We had reasonable success with the solder-through enamelled copper wire coatings, but generally still had someone on the production line dip the ends of the coil/transformer leads in a solder pot. One of the main reasons iirc was that we had difficulty transitioning the inspectors from through-hole soldering to SMT. Historical note: I believe that NASA demonstrated that certain bad-looking joints were actually equal/superior to the ones that inspectors were trained for. It was TOO hard to characterise the iffy looking joints so that they could be reliably distinguished from bad joints. When SMT came along various inspectors nearly had breakdowns :-)

[I have no idea of current practices; and gee, THAT was 25 years ago! Feels like yesterday.]
Hope you find out about that coating as I am rather interested too.

John K

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[Paul Andrews]

Maybe I should just ask digikey, which is my supplier in this case.

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[SWISSNIXIE - Jonathan F.]

Also, it would be possible that this is some kind of additional soldering component, to make the part suitable to use as a module, to increase the future solder point.

For example, if you want to use a chip on a small pcb, which is later machine-soldered on a bigger pcb, it can be a problem, if your part on the "Module" pcb gets molten too. For normal parts, is uncommon to be used as a module (solder), but for these chips, and other one, its quite common to manufacture modules.For example, the U-Blox Nina Module, is based on a ESP32

[Terry S]

My guess would be ENIG like on a PCB. Electroless Nickel Immersion Gold. The data sheet or the vendor's website would tell you the exact finish.

Terry

[Paul Andrews]

That was what I assumed until I reflowed it. I wish I had photos of what it was like before I used my hot air rework station to take it off and reapply it. The gunk cleaned off before I resoldered it.

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