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I am soldering a 10 lead MSOP (LMH1980) onto a PCB. Or trying to do so. The chip has a pitch of 0.5mm. I find that every time I use the "tack and glob" method I have been taught, I cannot remove the excess solder; it just sticks to the pins. (Tack and glob: pin a few crucial pins down, then glob solder over the pins. Wick away excess solder.) Tack and glob seems to work for a TQFP44 dsPIC and an TSOP16 ADG733 chip, but every time I do tack and glob on the LMH1980 I find that I cannot remove the excess solder, and in the process of trying to do so, I have damaged two PCBs (pulled the pads off) with components already on them. How can I solder this chip? BTW, I have only a basic temperature controlled soldering iron and hot air station (Aoyue 968.) Nothing fancy.

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  • \$\begingroup\$ what flux are you using? \$\endgroup\$ – markrages May 11 '11 at 19:58
  • \$\begingroup\$ Could it be that the pads extend too far under the chip? \$\endgroup\$ – starblue May 11 '11 at 20:07
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    \$\begingroup\$ Oh come on. I've got a Aoyou 968 too. I wouldn't call it 'nothing fancy'. 'Nothing Fancy' would be a trash shack firestarter. \$\endgroup\$ – ducksauz May 12 '11 at 4:38
  • \$\begingroup\$ @Ducksauz It's certainly no Weller but does the job. \$\endgroup\$ – Thomas O May 12 '11 at 6:35
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enter image description here

Flux!

Solder bridges mean you need more/better/fresh flux.

(Either iron or hot air will work fine. Heat is heat. I prefer iron for clearing shorted pins: wipe iron on sponge, apply to pins, repeat. The excess solder will stick to the tip.)

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  • \$\begingroup\$ More Flux always gets +1. \$\endgroup\$ – user3624 May 12 '11 at 2:15
  • \$\begingroup\$ What flux should I use? My supplier has about 10 million different types. \$\endgroup\$ – Thomas O May 12 '11 at 6:36
  • \$\begingroup\$ I use Warton Metals rework jelly: warton-metals.co.uk/re-work.html It's superb stuff! \$\endgroup\$ – Leon Heller May 12 '11 at 9:44
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    \$\begingroup\$ Those flux-dispensing pens are the most convenient for clearing bridged pins. \$\endgroup\$ – markrages May 12 '11 at 13:42
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Given that you have a hot air station, I think your best bet is to use a very thin layer of solder paste, preheat the board + chip (I used to have a recycled George Foreman grill for this) and then use the hot-air to push the solder past the melting point and allow it to flow.

BTW, do you have solder mask on your boards? At finer pitches, the solder mask can make a big difference on your success rate.

If you are going to tack-and-glob, make sure your glob is much smaller than usual. You might need to work with a much finer solder.

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BTW, for solder already stuck beneath and under pins, sometimes hot air with high air flow can push the solder away from the pins enough to clear the short. If your board is masked, there's a decent chance the resulting glob sitting under the IC will harmlessly stay put.

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    \$\begingroup\$ Another option for dealing with solder-bridges under the IC is to heat the chip and solder till ALL the pads melt, and then nudge the chip gently. It should move, and spring back into position, due to solder surface tensions, and with any luck, this should break or disrupt any connections under the device. (Note: this requires additional flux to work properly, solder doesn't have much surface tension when it is oxided over.) \$\endgroup\$ – Connor Wolf May 12 '11 at 5:44
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I've soldered similar devices without any problems. I use a very fine tip and a stereo microscope. I normally use drag-soldering with a mini-hoof cartridge and my Metcal system for fine-pitch devices, but I don't think it's suitable for one like that.

You can avoid damaging the PCB when removing parts like that by using Chip Quik.

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  • \$\begingroup\$ I can normally remove the solder, but I find that on these chips, solder gets caught under the pins and once it's under there, it doesn't want to come out. \$\endgroup\$ – Thomas O May 11 '11 at 19:57
  • \$\begingroup\$ Chip Quik should deal with that, all the solder is melted at low temperature. \$\endgroup\$ – Leon Heller May 11 '11 at 20:00
  • \$\begingroup\$ @Leon, nice idea... if only it weren't so expensive. Student budgets... :( \$\endgroup\$ – Thomas O May 11 '11 at 20:15
  • \$\begingroup\$ I think they'll send you a sample kit, enough for two or three QFPs. \$\endgroup\$ – Leon Heller May 11 '11 at 20:35
  • \$\begingroup\$ @Leon, yeah, but you need to pay for it... \$\endgroup\$ – Thomas O May 11 '11 at 20:50

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