Problems with switches soldering

[ar__systems]

I'm using GC10 lead free paste and pupulate boards with fair number of switches like these https://www.digikey.ca/product-detail/en/c-k/PTS645SM43SMTR92-LFS/CKN9112TR-ND/1146840

For some reasons some of the buttons are not soldered at all even though the paste fully melted. The leads are kind of sitting in an indentation of the pillow if solder in the end. Sometimes they just not connected at all and can be removed with no effort.

Should I switch the paste?

[ar__systems]

I've got some pictures. You can clearly see indentations from the leads on the pads. When reflown they look fine, they don't fall off on their own. But might fall of with just a little pressure... So annoying.

Any help?

[jmelson]

That's called head in pillow, a common problem.  Generally, it is caused by not getting the board and component leads hot enough for long enough for the flux to break down the oxide layer on the part.  With switches like that, they are probably real sensitive to heat, so you can't raise the temperature too much or the plastic might melt.  Really, the only things you can do are up the temperature or the soak time while the solder is at full liquidus, or to get a more active flux.

Jon

[zeqing]

check your buttons if they are oxided? and try to clear the pins by robbing.

[Jellysfish]

use a more aggressive flux?

[ar__systems]

So far I'm leaning towards bad batch of switches. Sourced from Digikey. Few days ago I populated prototype board with them and 7 out of 8 did not attach to the board at all, they fully came off with minimal touch. From now on I will apply extra solder paste on the pins if I use those again (I have a bunch of loose ones).

At the same time I assembled a small production batch of boards, using the same paste, same oven and settings, using new switches from China - over 1000 switches in total. No problems there.

[langwadt]

old and oxidized, that's the risk with components of unknown age and origin

[ar__systems]

No they were not old. I bought them couple of month ago for another batch of boards. I had tons of issues...

[tablatronix]

I have noticed switches are typically filthy, probably because they are bulk produced and stored. Active flux, or I wonder if you could tumble them somehow to clean up the metal, but not plastic bits.. hmm