PCBs: HASL, Lead-free HASL or ENIG finish?

[Deke609]

What's the preferred finish?  What does BH use for its boards?

I'll be using SMD components, in case that informs the recommendation. 

Not doing anything too exciting - just an "Instructable" build of a milli-ohm meter. The inventor has published the gerbers, so all I need to do is order them. Reported to be accurate to 0.1 mOhm and can be programmed to also measure mV [edit: uV].  Looks like a fun build and I figure it might even be useful for measuring small value resistors.

cheers and many thanks, Derek

[Paul Birkeland]

What will you be using to install the SMDs?

[Deke609]

A cheap computer based magnifier, 0.02 solder and a really fine, pointy solder tip.  I've read that solder wick can be used for some parts too - but I'm assuming that only works with HASL.  I have a bunch of fine solder wick as well.

cheers and thanks, Derek

[Paul Birkeland]

Do you have a link to the kit you're putting together?  You could probably get away with using an iron to solder surface mount resistors, maybe, but pretty much everything else is going to require using a different method.

[Deke609]

Thanks PB.

Two links:

http://www.danielrp.net/projects/proj-milliohm-meter-1

http://www.instructables.com/id/Milliohm-Meter/

[Paul Birkeland]

That's not something I would consider solderable with a soldering iron.

You will need a hot air station, or maybe you can use the hot plate method. I would strongly recommend ordering a stencil with the boards to help you lay down the solder paste properly.  Most of that stuff is lead free, but I would still use HASL. 

[Deke609]

Many thanks PB. I will look into getting all of that.

cheers, Derek

[grufti]

I am 67 years old. My eyes are not what they used to be when I was 25. I handsolder SMD parts with the pitch of your IC3 quite regularly. I sometimes use solder, sometimes paste, always decent amounts of flux. I also can't do it without good light and magnification.

You can see at least one recent SMD project that I handsoldered on diyaudio, same user name.

I can actually work faster with SMD parts and I prefer it. I even use a relatively large tip that I angle to get to the spot.

[oguinn]

I tried the Schiit Coaster amp, and that was all SMD. Never could get it to work when soldering with an iron, and I didn’t want to buy a bunch of new equipment for one project.

I hate SMD. Best of luck.

[Deke609]

Thanks grufti and Jameson -

The only thing that really gives me pause is that chip with a ton of tiny legs that looks like a metal millipede (the "IC3" that grufti refers to?  I'm unfamiliar with SMD nomenclature). Not sure that I could pull that off with a soldering iron. Maybe if I use a stencil and paste and then heat each leg with fine soldering tip?  Any thoughts/recommendations on this are welcome.

I usually like buying new gear, but I'm hesitant to invest in a hot air station. At least right now.  I've mostly sworn off buying cheap "starter" tools b/c I inevitably end up later buying a well-made one and giving the first one away - completely undermining the "economy" of the first purchase. So the purchase would be pricey.

I wonder whether a regular heat gun -- the kind used for stripping paint, etc. -- might work? I have a good one, adjustable from something like 350F to 1300F with low and high fan speeds.  It looks like after-market nozzles are available online that might get me an approximation of a hot air station. Anyone tried that?

Failing that, I will consider getting a hot air station. I've been steadily working on getting my son interested in STEM stuff (fyi - for those with kids or grandkids: watching Battlebots videos got my son hooked on fantasizing about robot designs and the metal carnage he hopes to one day wreak upon competitors -- although the glean in his eye noticeably lessened when I told him that building a similar contraption would require a lot of physics, engineering, math and programming know-how). So maybe a rework station wouldn't go to waste. But I can't see it being all that useful for my diy audio interests - I'm too much of a tweaker/rebuilder and need point to point.

cheers and thanks, Derek

[Paul Birkeland]

I got the garbage hot air rework station on Amazon that's less than $15.  If you turn it up all the way, it melts itself, but otherwise it's usable.  That and some chipquik paste and flux got me far enough along to complete a bunch of surface mount projects.  Good tweezers are nice too.

[oguinn]

I did use a heat gun like what I use to strip paint or shrink heat shrink and it worked well enough with chipquik, but the problem is that even on its lowest setting it was blowing tiny components all over the board.

I guess I drink too much coffee, too, because my hands were too shaky to place things that small and have them stay put.

I'm with you, though, Derek. Having bought enough things a bunch of times in incremental steps up in quality (e.g., three soldering irons, three sets of wire strippers, etc.) I'm not really interested in buying cheap tools for one project. I either bail on the project or find enough other projects that an investment in quality tools is justified.

[Deke609]

Thanks PB. Are you referring to the little handheld air guns used for shrink tubing etc.? Those are the only really cheap hot air guns I can find on Amazon. I have one of those. I just looked up the reaction temp of chipquik and was surprised by how little heat is required!  So it looks like it might work. Worth a shot, since I already have one.

@Jameson - yeah, I'm in the same boat. Cheap little tools are wasteful but at least they don't take up much space and come in handy when you can't find the good one in the pile of parts and tools on the bench.  But what really swore me off "starter" tools was the bigger stuff: router, chop saw, circ saw, drill press, etc.  I stopped buying really cheap versions of that kind of stuff 10+ years ago. 

cheers, Derek

[Paul Birkeland]

Thanks PB. Are you referring to the little handheld air guns used for shrink tubing etc.?

No, it's a hot air soldering station, not a heat gun.  Do not use a heat gun, it will blow all your parts all over the place and probably blow your molten solder paste right off the board.  It's the wrong tool for the job.

[Deke609]

Many thanks PB. Hmm. I watched a couple vids about using solder wick to deal with tricky ICs and it looks doable. I'll try this method first. And if that fails, I'll get a hot air station.  I'll have 5 pcbs, so there's room for some failed attempts.

cheers, Derek