Anyone familiar with SMD reworking?

C_Mababejive

I need to do some SMD repairs...are there any professionals or competent DIYers reading?
ta

aerostar

It would help if you gave a location and what exactly needs to be done.

C_Mababejive

I need to extract a series of SMD electrolytic capacitors from a double sided PCB designed for SMDs. I am wondering whether it would be easier/better to clip the cans of the caps off so that the tags are exposed and then desolder the tags rather than trying to desolder the cap complete thus potentially risking pcb track lift.

Tools in use, fine tipped 40w soldering iron. No specialised gear..

Ta

spannerzone

If you can solder with a fine tip iron then it's perfectly feasible to do 'some' soldering repairs/reflow to SMD components, all depends on what it is you've got that needs doing.

There's some useful guides on Youtube, I found EEVblog on Youtube had some useful, if not a bit long winded videos to watch (and providing you can put up with the Ausssie's rather high pitched voice) - you can learn quite a bit from this guy if you have the patience.

neilwoods

More likely to damage the tracks by cutting the ends. Simple soldering iron and de-solder pump or braid will be fine.

Or buy reflwork machine from amazon for £40

fwor

Electrolytics are one of the hardest to deal with, because usually most of the body sits on top of the solder pads. If you try to desolder them one side at a time the leverage on the other is too great and the track lifts.

Last time I needed to do this I made a forked soldering iron bit (out of the remains of a 13A mains plug pin) which would make contact with both solder pads at once. It worked, but was very fiddly, and only works if all the capacitors are the same size...

epninety

Agree that SMD electrolytics can be tricky to deal with - I have a hot air rework station, but for just one or two I'd probably still do the job with two soldering irons.

- Make sure your irons have a small enough tip that you can actually get contact on the pads

- Don't be afraid to add solder rather than remove it - the extra metal thickness conducts heat under the body much better.

- Try to heat both pads at the same time, then the cap will either lift off between the tips, or just drop off.

Pitchshifter

epninety wrote: »

Agree that SMD electrolytics can be tricky to deal with - I have a hot air rework station, but for just one or two I'd probably still do the job with two soldering irons.

- Make sure your irons have a small enough tip that you can actually get contact on the pads

- Don't be afraid to add solder rather than remove it - the extra metal thickness conducts heat under the body much better.

- Try to heat both pads at the same time, then the cap will either lift off between the tips, or just drop off.

Yes, 2 irons with chisel tips. Ideally you also need a vice to hold the PCB upright in a vertical position (on edge), then use gravity to allow the caps to fall off as you heat both leads.

Expert technique: In the past I've actually managed to remove SMD caps easily with just one soldering iron, by rapidly flowing extra solder on each side alternately back and forth. It's tricky but can be done.
Solder braid and flux paste to level the pad after removal.

C_Mababejive

Yes,i was thinking that gravity might provide a solution and i had noted there could be difficulties due to the cap pads being mostly under the can. I'm just wondering if i can apply a slight pull load to the cap can and heat the connections. They are too tiny to grip with my index finger & thumb as id likely burn my fingers badly with the iron. The problem is that some of the caps on this sub-assembly are showing signs of leakage as i suspect they were under specified so im looking to remove, clean up and replace...

Pitchshifter

Just wondering, what is the board your trying to repair?

Here's another technique you could use if you're very careful. It involves fatiguing the leads until they break by wiggling the can.

worth watching the whole video for tips on this technique.
http://youtu.be/Y1l7qSezFDQ

Joe_Bloggs

Consider this approach if you can get the component to support the weight of some cross grip tweezers.

If the tweezers were initially hot or later made to be hot then heat will flow from the tweezers to the component and then to the to the solder and both should fall off once the solder is liquid and can no longer support the weight of the tweezers and component.

This method avoids the temptation to yank at the assembly before it is free to come away.

Should the component catch fire or explode then there may be more access to the concealed pads or possibly a trip to casualty if safety precautions were not taken.

Next episode Ball Grid Arrays . Use the Grill or the Oven ?.

J_B.