Lead Free (RoHS) paste recommendations

[loki42]

I'm contemplating which lead free paste to use for production. It'll be with stencils and a (very) basic oven. Low volume (100s not 10000) of units, some QFN no BGA, 0402 smallest parts. I'm using 100C for hand soldering which is great, but contemplating the SN42/BI57/AG for pastes.  Boards are ENIG if it matters.

Should I got 100C, SAC305 or the Bi stuff?

[jmelson]

I'm contemplating which lead free paste to use for production. It'll be with stencils and a (very) basic oven. Low volume (100s not 10000) of units, some QFN no BGA, 0402 smallest parts. I'm using 100C for hand soldering which is great, but contemplating the SN42/BI57/AG for pastes.  Boards are ENIG if it matters.

Should I got 100C, SAC305 or the Bi stuff?

100Sn can be brittle as well as prone to creating whiskers, so I would avoid it.  It isn't a whole lot cheaper, anyway.  I have had quite good results with the SAC305, but the secret is in the FLUX, not the alloy.  I got some great stuff from Warton Metals in the UK, but it is really hard to export to the US.  You might have a distributor in AU for it.  I have just started using Loctite GC10 (might be sold under the Henkel brand there) and it appears to work VERY well.

It was suggested by my board manufacturer to use some electroless gold flash when I first went over to lead-free, and it was an absolute disaster!  If the lead soldered to the pad, all was fine, but if it failed to solder, rework was an insane catastrophe.  I think this was a case of "black pad".  The only way to fix that connection was to bend the component lead up, scrape the black deposit down to bare copper, tin it, and then bend the lead down and solder.

So, I have been using lead-free HASL ever since, and it works quite well.

Type 3 paste has very coarse solder beads, type 4 is finer, type 5 is yet finer.  Type 5 costs a lot more, so I am using type 4 now, and it seems to avoid solder bridging.  I think the last stuff I had may have been type 3 -- a mistake.

Jon

[loki42]

Mmm... all my current components, board, tips etc are all 100% Pb free, never touched it but I was planning to use some old soviet germanium diodes in this circuit. Is there any way to tell what the pins are made from? Will they contain Pb?

Otherwise SnBiAg sounds pretty good mostly because it gives me so much safety margin with the dodgy cheap reflow oven. I'm not doing any BGA.

[mrpackethead]

Cab't say enough good things about Henkel GC10.,, its SAC305 and its just so easy ( in comparison ) to other pastes, Its nearly twice the price as some other brands but it just works so well, and 500g of paste makes a lot of boards.

[TJ232]

+1 for Loctite GC10.

More expensive than others but as soon as you will use it it will be hard to even think to use anything else.

[SMTech]

Interesting so many have tried Warton,  the biggest difference I see with Warton is a feature they are very proud of which is very shiny very silvery joints, the flux in many others can result in a duller finish and quite yellow flux residue. They seem to achieve this with both the 2010 and Nexus, I find the flux somewhat more sensitive to overpasting (either by application or pad/stencil design).

I always had excellent results with Henkel/Multicore but don't think we tried GC10, I think we switched to something more open to abuse before they released it. BLT have a similar paste (in terms of shelf life and abuse) that I find works very well.

The best paste I have trialled is from Almit, but it is seriously expensive.

If you ever have the fun of a Solder rep coming round they all tell you the same thing, broadly speaking, there are two approaches taken to flux development, America tends to focus heavily on the end result being ridiculously textbook perfect (which may also be why they seem to be less fond of no-clean). European/Japanese style pastes focus on what the paste is like to use.

Even with 100s of boards don't forget that fumes from Rosin/Colophony is pretty nasty stuff so ventialting your oven or reflow area is a good idea. Of course the same should be true for manual through hole soldering but at least in that instance there are several colophony free solders you can use.

[loki42]

GC10 sounds like the thing to use. SnBiAg does give me a nice window between melting the plastic connectors and reflow though. It seems a lot less tested in production. Only annoying thing is the giant size containers so I can't try out 3 different ones easily.

[SMTech]

SnBiAg does give me a nice window between melting the plastic connectors and reflow though. It seems a lot less tested in production. Only annoying thing is the giant size containers so I can't try out 3 different ones easily.

Its more than "not just tested in production" it is a speciality paste for specific low temp reflow requirements, it isn't intended as a drop in replacement for something like SAC305. It is more brittle, more susceptible to cold and cannot come into contact with lead which can drastically reduce its melting point. That means no old stock parts, no HASL and no sneaky reworking with leaded pastes.

[loki42]

What do you mean by more susceptible to cold? GC10 appears to be right near the top of what my toast oven is possible of temperature wise but I'm planning to buy some and try it. If it doesn't work then I'll have to go for the lower temperature stuff.

[mrpackethead]

I do a lot of paste in pins for connectors, and feel your pain.

(a) I use vapour phase. This means it only ever gets to 230C.
(b) Its going to be a lot easier looking for connectors that can handle the heat, than finding relaible paste for low temp.   

[loki42]

Thanks for all the recommendations for Loctite GC10. I did a test run of a little board yesterday that worked well in my little ALDI toaster oven and I've just done my first full large board. I haven't tested the board yet, but it all looks great. I didn't melt the FPC connector either!