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need advice for desoldering SMT

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Buriedcode

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use a rework station

Hi,

Although my soldering skills are pretty good as far as through hole, and SMT when actually soldering a NEW device to a NEW board, I made a complete mess of a motherboard I was working on :( Had to replace an EEPROM.

I would like to be able to desolder SMT parts, both passives and IC's (SOIC, SSOP, nothing tooo big like 512 BGA) but I really can't afford an expensive reflow station. I'm currently unemployed and money it very tight, plus I'm really just a hobbiest. So, after some research on the net, I was wondering:

Would a gas/butane soldering iron fitted with a hot air nozzle be good enough for desoldering SMT parts?

I'm new to 'hot-air' work, but I think its deffinately the best way, since I've lifted more pads than I care to remember using my 12W with 0.8mm tip. And desoldering braid doesn't get all of it off. So I want a 'reliable' way to remove and resolder parts with minimal damage to a PCB, and preferably under $40US (thats £30 UK).

Also, another little question:
Does anyone know a good way (and again, cheap) to replace a SMT pad for an SOIC. I lifted it and it broke off the tiny 4mil track it was on. I've scraped away the solder mask to give me access to the track, but obviously soldering a wire to it is impossible. Any ideas would really be appreciated!

Any advice would help, since I've got a load of SMT things to rework for a friend and time is short.


Thankyou,

BuriedCode
 

jdhar

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desolder smt

For rework, if you have a hot air gun, that is best. But you have to be careful when blowing off parts around the one you want (small resistors). If it's in a dense area, this will not work.
Next, if that doesn't work, one trick I do is to short all the pins (assuming SOIC/TSSOP , similar) together, and get two soldering irons, and heat both sides of the shorted IC simultaneously. The solder will all melt, and since it's all shorted, the IC should lift right off. If you have a TQFP, heat gun is probably your only choice. Lastly, and this is worst case, gently lift pins from the IC. Lift all the pins on one side, and then bend the IC up - for the other side, run the iron really fast across the side until it's all molten, and it should come off.
Hopefully this helps.
 

    Buriedcode

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fuzzzy

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desolder smt parts

If you decide to use hot air(the best and only way for some chips) you should protect components around the one to take away.you can use adhesive paper to create a mask and you have to lift the component gently in order not to take away pads not melted.

To recover broken pads, if too small to drive a wire, you can try to use a conductive ink.
 

    Buriedcode

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nandopg

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desoldering smt techniques

Dear friend,

I have all the time to work and rework on SM boards pretty compact and squeezed and actually none of these special tools work there.

All I use to work and rework on SM those boards is:

1) A good quality microscope. You can buy those for maybe U$300,00 on E-bay.

2) A sharp cutting tool

3) Two different size of Braids to clean up the solder.

4) Flux

5) Two regular temperature controlled soldering stations.

6) A hot plate.

7) Q-tips and isopropylalcohol

When I have to replace an IC I just cut all terminals close to the its package and then I clean up the terminals and the solder on the pads with the braids. That is true that the component you took out is gonna be out of service but the board suffers a minimum of stress.

To rework on passives I use two irons, one on each hand. If one side of the component is soldered to a solid ground plane I adjust the temperature of one of the irons a little bit higher. If it is possible I heat up the board using the hot plate up to about +80C to help the desoldering. After the extraction of the component the pads should be clean with the braid.

When I finished the pads clean up with the braids, I used to clean the remaining flux and solder splashed using some Q-tip wetted with isopropylalcohol.

The last, I do all the work under the microscope. If you follow these guide lines you will have 100% of success at a minimum cost.

NandoPG
 

    Buriedcode

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Buriedcode

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component stress hot air desoldering

Hi again,

Thankyou all for your reply's!

Its interesting that there are many techniques for both soldering and desoldering SMT, and its always reasuring when people discuss their experiences with these techniques. It allows me to gauge what I really need for the type of work I'm doing. Thanks again!

Reading through, its seems that I have a few things missing from my setup, and my technique. This is probably why I've ruined boards/components :( I've set aside £30 ($40USD) for my equipment, first on the list is 'flux', as I never use extra, I just rely on the core in my solder, which probably isn't enough. Then its magnification, I've got a magnifying lamp somewhere. And then its other consumables: solder wick, solder paste (when I get my gas iron), low temp solder, and eventually a temp controlled iron.

Hope you don't mind, but I've copy/pasted your advice to a text file for future reference :) since I want to try all techniques to see where and when they should be used, and if it 'works for me'.

Also, TheHungry, I signed up with AVRfreaks, and that really is a great article! I'm about to order a gas soldering iron for rework, and then practice on some scrap boards to get me up to scratch.

Thanks again, you all provided very useful information, which on the web, is nearly always given by a company trying to sell their product. Impartial advice is a rarity these days.

I might post back in this thread once I've got all my equipment up and practiced like mad.

Buriedcode.

Ps. I started soldering 5 years ago, and I dread to think how many mistakes I've made, hopefully, thats in the past.
 

lrpa

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butane soldering iron ssop

Use a rework station or hot airstation + magnifying glass
 

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