Need advice in using a rework station

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Fisher
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Need advice in using a rework station

Post by Fisher » Sun Oct 08, 2017 4:52 pm

I recently got a Uni-T 881D rework station.
Image

I just tried it with some board on my "junk pile", and after I tried to disassemble a cartridge.
Unfortunatelly, I burnt the PCB a little:
Image

I need some tips on using it, specially by the guys that probably have used rework stations before in the way I'm supposed to use.
Also, when putting back the removed ICs should I use a desoldering pump or there's a way of doing it with the hot air?
Thanks in advance!

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TmEE
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Re: Need advice in using a rework station

Post by TmEE » Sun Oct 08, 2017 11:17 pm

High heat, high airflow, good distance (5cm+) and small amount of time in one spot is needed to prevent burns on the board. Through hole componets are not easy to remove with hot air, for best results you want to alternate between heating both sides of the board and even then you risk of damaging the board. I personally use a solder sucker + regular iron to remove through hole parts if preserving PCB is critical.
You can forget about using heatgun to put the chips back. Use a solder sucker to clear out the holes, place chips back and go over each pin one by one with regular iron.
For surface mounted parts you can do both removal and putting back with a heatgun very easily (but I still prefer regular iron + "knife" tip for putting back).
Last edited by TmEE on Mon Oct 09, 2017 7:22 am, edited 1 time in total.

lidnariq
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Re: Need advice in using a rework station

Post by lidnariq » Sun Oct 08, 2017 11:40 pm

I haven't personally yet started doing hot air rework, but maybe this article, its comments, and the video it links to could be useful.

Garth
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Re: Need advice in using a rework station

Post by Garth » Sun Oct 08, 2017 11:40 pm

I see TmEE posted while I was writing. I'll post anyway, further supporting what he says.

When I worked at TEAC we had expensive desoldering pumps, but they were always more trouble than they were worth, so I went back to the spring-loaded solder sucker. In the case of many of the holes I see in your second picture (the first picture doesn't show), I'd actually add solder to the hole first to get better heat transfer from the soldering iron and completely through to the other side, then stick the solder sucker on it and push the button very quickly before the solder has a chance to re-freeze.

If a hole goes to a ground plane, with little or no thermal relief, those can be pretty stubborn. Just about the only thing I've found that works is to put the soldering iron on it from the back, with enough solder to fill the hole, and bring it up near my mouth and blast it out with a forceful blow. Since tiny droplets of solder will splash out the other side, you'll want to make sure that there's nothing sensitive to those behind the board.

Solderwick can be used for final clean-up, but if you start with that it usually won't clear out the hole well enough to get the leads of another IC into it.

Since 1992, I've been working for a little company that makes audio communications equipment for aircraft, soldiers, law enforcement, medi-vac helicopters, etc.. I do all the electronic design work. I also do the occasional repair on our high-end intercoms, with boards sometimes up to 12 layers and 500 parts. Four of those layers are ground-plane layers (to stop crosstalk from capacitive coupling in high-impedance audio circuits), meaning it's hard to get the heat to a hole well enough to clear it out. The board is very valuable; so in the rare case that an IC needs replacement, or needs to be removed to replace a part underneath it (yeah, our boards are super dense, with up to 11 resistors and diodes staggered in five rows underneath a 14-pin IC), I cut all the leads and remove them one by one rather than trying to heat the entire area of the board up and pull the IC out intact. That's for thru-hole obviously. In recent years all our production has been surface-mount except for connectors which have to take a lot of force; but the older thru-hole stuff will still be serving in the field for many more years.
http://WilsonMinesCo.com/ lots of 6502 resources

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Fisher
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Re: Need advice in using a rework station

Post by Fisher » Mon Oct 09, 2017 6:39 am

You guys are great!!
I'll look carefully the suggested links and do some practice to see how good I can get on it.
Thanks!

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