<d1b2>
<gimbas> currently trying to assembe some glasgows, but i'm having issues with the bga, do you guys just put paste on the board and place the fpga on the paste with the original balls? i'm using leaded solder paste.
<d1b2>
<gimbas> maybe you could help me @esden since you've done your share of smd assembly i believe
<miek>
yes, but i use lead-free paste to match what's already on the bga
<d1b2>
<gimbas> hm, but i don't have lead free
<d1b2>
<gimbas> you think the mix would cause issues? never tried it for obvious reasons
<d1b2>
<h0m3us3r> I didnt assemble glassgow, but my usual procedure for bgas is not use paste at all, just some tacky non-bubbling flux.
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<d1b2>
<atx> Oh hm, there is tacky and not-tacky flux?
<d1b2>
<atx> Oh apparently not-tacky flux is just a very liquid, almost watery, flux, never seen that used for electronics.
<d1b2>
<atx> @gimbas iirc if you mix lead and tin in the wrong ratio, you get crystals of lead suspended in tin
<d1b2>
<atx> Which is probably not what you want
<d1b2>
<atx> We had this picture in our solid state physics class
<d1b2>
<atx> (3) is where you get crystals of lead in tin
<tnt>
Mixing leadfree/leaded is fine for prototype, it's just not ideal. You also need to heat the board more than the ideal temperature for the leaded flux.
<d1b2>
<atx> So the alloy gets fucked as it cools down
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<awygle>
i second the no-paste suggestion for BGAs
<d1b2>
<atx> I used no paste last time I did BGAs and still got shorts
<d1b2>
<atx> Can't imagine adding paste would make it better
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<d1b2>
<h0m3us3r> Probably wrong/not enough flux
<d1b2>
<h0m3us3r> I solder like a monkey and still barely have any issues