Almost got a black eye here on a prototype. Ordered a bunch of large boards at Advanced Circuits and it turns out that the free upgrade to lead-free finish is actually a default that cannot easily be changed. IOW you can normally not decline this "upgrade". However, they were very understanding that we really didn't want lead-free and will now do our protos as production runs. No idea why we go RoHS here in the US now (this is a company that actually produces in the US).
Anyhow, just wanted to let you guys know about that before a nasty surprise happens to you.
I've got some prototypes from them a couple of weeks ago. Looks like regular leaded solder to me... I didn't ask for anything specific, they just came this way by default. But mine are all thru-hole...
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Some of the coatings are ok, some (like white tin) are awful. The good news is that lots of people are now offering gold plating at the same price, and that solders beautifully. The bare boards don't tarnish and look like jewelry, too.
Gold plating I feel is the best approach, but be careful, as some companies are asking 25% more. If you can get them at the same price, great!
I see the future being RoHS, as most companies will eventually gear up for world wide sales. Sales don't have country borders these days. :-)
Don...
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I probably could have gotten gold coating but I had to make a split-second decision. The Gerber review took their engineers a while and it was getting close to 6:30pm in Colorado. Next time I'll try gold.
Elect. gold is our new standard. It doesn't look as rich as the old gold plated boards, but it's still nice.
Best regards, Spehro Pefhany
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However, there is a lot of gear that is exempt and many of the parts for specialized equipment cannot (yet) be purchased RoHS compliant. Even for some on this board that come in RoHS such as data converters I found that there was no stock anywhere for the RoHS edition. Had to buy the tin-lead versions.
No surprises - assuming HASL, they work fine using normal leaded solder. This includes soldering with irons, wave and reflow methods. It does not change the process hardly at all. The leaded solder just dissolves it, creating a slightly non eutectic solder (closer to 60/40). It's the same with tin plated parts which have been used for quite a few years, other then lead free BGA's. The downside is you have a possibility of tin whiskers forming in areas that have not been wetted with the leaded solder. The tin whisker risk is somewhat dependant on the alloy used for the HASL. Tin dendrites are from currents forming in moisture and can be avoided. White tin is really bad, as it compresses the surface during plating and causes rapid tin whisker growth. We've done many thousands of boards with lead free HASL without much issue.
Gold plating (ENIG) is bad, as it is a flash of electroless gold deposits a few atoms thick, over nickel which is plated over the copper traces. The gold is sometimes hard to wet (BGA's for one - they are so bad we pre tin the pads). The intention of the process is when applying solder it dissolves the gold, thus wetting the normally difficult to wet nickel. You now have a solder joint with a little gold in it, which if in high enough concentration causes the solder to go brittle. The nickel to solder intermetallic layer is poor and is prone to cracking (a well known repair problem in the repair industry). I think the copper to nickel bond is ok, but I never really looked into it in much detail. Other problems that can arise is weird thermocouples from all of the dissimilar junctions. This would have been a potential problem with some research I did awhile back where were measuring temperature from a thermocouple with a resolution of around 1/1000 of a deg C. The thermocouple was so sensitive you could peg the graph by breathing heavy several feet away!
Thanks for sharing your experience, Jeff. Maybe HASL would then be an option for us, as long as we wet everything. The latter could be a problem in thru-hole areas such as DIN connectors.
ENIG looked a bit scary to me from the beginning so I politely declined when they offered. The nickel-copper is generally good though for mechanical stuff, I have used that a lot for shield mounts and the like in order to avoid dissimilar metals touching (nickel plating the shield studs a well).
Thermocouples would spell disaster for this circuit as it relies on microvolt level DC paths to be stable.
Per the Nasa tin whiskers info collection, it isn't just tin that forms whiskers, it is just about every lead-free alloy and metal, just some more than others.
Proper through hole has solder wetting to the top. Problem areas could be untented vias, mounting pads and holes, etc. Basically if its not a pad, don't leave it exposed to become plated with solder in the HASL process.
OSP (bare copper with an organic protector) might be another option and it's cheap, but comes with it's own problems.
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