SnBi solder paste - Page 1
Forum section: electronics / general

author: SiliconWizard
author_rank: Super Contributor
timestamp: February 18, 2022, 09:05:08 pm
content: Does any of you have experience with SnBi solder paste?Are there any known reliability issues?It's lead-free, but is it RoHS compliant?Thanks for any input.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 18, 2022, 09:26:07 pm
content: I don't believe bismuth is on the ROHS list.

author: khs
author_rank: Regular Contributor
timestamp: February 18, 2022, 09:59:01 pm
content: I use SnBi (TS391LT50 from Chip Quik) since several years, it has a quite high surface tension so even if the print of the solder paste is not perfect the resulting solder points are quite fine in most cases (0.5 mm pitch).Regarding reliably I've seen no problems, but I would not use it for boards with power devices on it generating a lot of heath or boards with mechanical stress.

author: 48X24X48X
author_rank: Frequent Contributor
timestamp: February 19, 2022, 02:43:17 am
content: There are 2 type I believe, the lower temperature and the medium temperature. Even the solder paste manufacturer in China don't recommend me the lower temperature version unless it's not a critical application. I do however use the medium temperature Sn64Bi35Ag1. For general use, it is okay else I would use my SAC305 for other more critical products.

author: jmelson
author_rank: Super Contributor
timestamp: February 19, 2022, 07:02:37 pm
content: We found that they were fairly brittle, and lacked mechanical strength. Perhaps we did not have the right temperature profile for soldering, though.Jon

author: exmadscientist
author_rank: Frequent Contributor
timestamp: February 20, 2022, 09:22:00 am
content: All Bi-containing solder is going to be brittle to some degree. It's just the nature of bismuth, no way around this one.This stuff ought to be fine on the bench, but I'd keep it far away from production runs. I seem to recall Lenovo tried to implement SnBi solder a number of years ago. The speculation at the time was that they may have wanted to gethigherfailure rates for the usual nefarious reasons....

author: miken
author_rank: Regular Contributor
timestamp: February 20, 2022, 10:51:34 pm
content: I've done one small board with Chipquik SnBiAg, bunch of TSSOPs mostly. I'm not sure why but all of the joints came out a bit "puffy" so next time I'd reduce the stencil apertures. This was with a mylar stencil from OSH Stencils. Just a bench proto so no longevity considerations. I think I recall when touching up with an iron it wouldn't reflow that nicely, and it was easier to take it off and dab a bit of paste on, which would flow when heated. It's been a while though.HP published a document about SnBi that is summarized in an Indium corp whitepaper that searches up pretty easily. My takeaway was that it can work out close to SnPb mechanically, but back in a pre-RoHS world it would've been hard to keep lead from getting into your SnBi process and compromising your joints.I got curious about SnBi since I found it hard to get the sweet spot temp for standard lead-free in my toaster oven conversion, and would end up with toasty boards. I'll probably experiment more with it at home but putting it into production sounds like a lot of homework.