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SN100C wetting problems

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SN100C wetting problems | 13 July, 2007

Dear all,

we are using the lead-free SN100C solder alloy for wave soldering. We are experiencing wetting problems each time we have to solder a thick board or a board with a large ground plane.I think that maybe we are not using the right flux.

I would like to know which flux could give me good results with this alloy? Also I would like to know if there's other manufacturers that have same problems as ours.

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SN100C wetting problems | 13 July, 2007

There are a lot of areas that could be leading to this problem. We have some of these issues on some boards with this solder as well but the hole fill still meets IPC class 3 requirement of 75% vertical hole fill. Through hole diameter is important. Too small a hole will kill your ability to fill. Wave dwell is also very important....

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SN100C wetting problems | 13 July, 2007

As in more dwell?

We see the same problem with through holes connected to power or ground planes. The solder reaches the plane and stops. We are having our boards re-designed to increase the thermal relief and expand the hole size. We are also trying to switch to SMT wherever feasible.


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SN100C wetting problems | 13 July, 2007

We've experienced this issue with SN100.

A couple of things we've tried, all with varying levels of success: 1. Longer pre-heats. We use SN100 in a solder pot, and pre-heat the boards on our wave machine. This did have a positive effect, but I never measured top-side temperatures, so I can't quantify it.

2. Switch our boards to ENIG finish. Boards with white tin finishes seemed to give us worse results in soldering...less wetting, less top-side flow. ENIG boards did not exhibit as many of these issues.

3. Cleaning boards pre-processing. Every day. A quick alcohol bath to remove any contamination on the boards also improved our wetting and top-flow.

cheers ..rob

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SN100C wetting problems | 16 July, 2007

I have zero experience with SN100c, but hey, how much different can it be from Sn63Pb37?!

We solder large connectors all the time - sometimes these connectors reside on a ground plane area.

We've been able to overcome hole fill issues (on 63/37) through tried and true wave tweaking techniques - increased flux & increased dwell. Sometimes dwell times should be in the 3-4 second range (instead of the usual 1.5 to 2), and you really gotta pump the solder up there!

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SN100C wetting problems | 17 July, 2007

We haven't used no-lead yet so I can't speak to the specifics of that part of the equation, but am I the only person here that sees "thick board or a board with a large ground plane" and immediately thinks this is a thermal issue? Am I oversimplifying this?

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SN100C wetting problems | 17 July, 2007

You want to know which flux will over come thermal mass problems? That's easy - none.

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SN100C wetting problems | 19 July, 2007

SOOOO true!!!

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SN100C wetting problems | 19 July, 2007

You need to dwell the boards longer in the wave as the board is the largest heatsink. Just make sure the flux can take the longer dwell times anything up to 4 - 5 seconds so you may have to shallow your angle as well to around 5 - 6 degrees this will be a trade off for improved wicking/more bridging with shallower angles Best of luck

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SN100C wetting problems | 31 July, 2007

Well, everyone has provided good advice, but if you are looking for a wave flux that can provide much better dwell times and consistent wetting throughout the hole fill, without making adjustments to your production process, I suggest going with Senju's wave flux.

Senju wave flux is a rosin based flux, which produces much better wetting results, especially within hole fill. The only problem the rosin-based flux will pose, is with cleanability. Rosin based fluxes can leave much more residue then a water-based flux, but the benefits are evident. However, Senju does provide rosin-based, low solid content, wave fluxes (leaves much less residue, 7% solid content, and the residue is softer for probe testing)...

Is this a no-clean wave solder process, or water soluble? What type of wave flux are you currently using?

Another option would be to use a better alloy composition. SAC alloys will help with wetting as well as helping with reliability because you have less copper dissolution...

Sn100C is very cost effective in the beginning of your production process, however if you can't nail down the perfect production method for each product build, you end up spending allot of money on initial production/analysis costs and for reworking your boards later (labor); Even if you have your process down, your wetting may not be ideal and you will still have to go back and rework everything... In an ideal world/process, Sn100C will save you allot of money, but things aren�t always so idealistic, and people/production teams sometimes need a bigger standard of deviation�

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