Hi all,
I have a small surface mount amplifer/filter chip on a packed PCB that I need to replace. In order to solder in the new one I obviously need to desolder the old one first being as careful as possible not to damage anything else on the board. I've never desoldered before and was wondering if someone could give me the basics or atleast point me to a tutorial for desoldering in this type of application. Thanks so much for any advice,
Kev
On Mon, 18 Dec 2006 11:09:27 -0800, kevin.pavin Has Frothed:
-- Pierre Salinger Memorial Hook, Line & Sinker, June 2004 COOSN-266-06-25794
What type of package?
It's often worth crunching up the faulty chip with cutters to remove most of it before applying heat. Sounds brutal but the important thing is not to damage the PCB and prolonged desoldering is likely to. Once you've reduced it to just the soldered 'tails', remove each one individually using solder braid.
--
*If I throw a stick, will you leave?
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
If you really have no experience of desoldering, then I would venture to suggest that you are dicing with death to attempt successful removal of a surface mount chip on a packed board, as a first project ...
You really will need to practice first on a scrap board. I usually start by flooding the pins with new solder, then wicking off as much as possible. This will remove much more solder than just going for it with the existing solder, which will not melt and flow up into the solder wick very well. I then slide a length of single strand rework wire under all the pins down one side, and tack solder the end to any convenient solder pad. If you then gently pull on the free end of the wire, away from the chip body, whilst applying heat to each pin in turn, they will come up off the board cleanly, as the wire passes below them.
When most of the pins are separated from the board, you may see the chip body start to move. Be careful then that the removal of the last couple of pins does not twist the IC and pull the last couple of pads off the board. If you do not see the IC moving, it is likely glued to the board. The glue bond is usually easily fractured by inserting a blunt scalpel blade under the edge of the IC body, and twisting. When the IC is off the board, re-wick the pads to make sure that they are very flat, and remove any traces of glue.
Position the new IC very carefully, making sure that it is the right way round, then tack two pins at opposite corners. Check the pin alignment again with a strong magnifying glass. When you are satisfied that it is aligned correctly, apply some liquid flux to one row of pins, then just go ahead and solder with the smallest iron tip and finest gauge solder that you have. Don't worry about solder-flooding bridging the pins at this point. If you are using a good quality liquid flux, this should be minimal anyway, if you are not going mad at applying solder. Repeat for the other one or three rows of pins, depending on package type.
When you have finished, examine your work with your magnifying glass again - a jeweller's loupe is ideal for this - and then go back to any pins that have bridged, and apply your solder wick with your iron tip to the vertical faces of the affected pins. This will remove the excess solder causing the bridge, without compromising the joint. Clean down with flux remover and an old toothbrush, and recheck the work with the magnifier. You should find that the job you have done is nearly as good as the original flow soldered product.
Arfa
wrote in message news: snipped-for-privacy@80g2000cwy.googlegroups.com...
Hint for de-soldering surface mount ICs. Use a hot-air paint-stripper,1400W,500 degree centigrade,with 2 level heat control to prolong element life. Form a ring of silicone covered wire around the IC{to isolate the remaing components on the pcb.Push a thin piece of wire under one side of the IC and form a loop around the IC,repeat on the other side;this is to remove the IC when the solder melts, tug on these wires while heating up to ensure minimum heating contact time. Place a slab of PTFE with right size hole cut into and clip pcb and slab together with clothes pegs/Bulldog clips etc. If the IC is for re-use then cover body of IC with heat insulating material or blast IC with freezer spray.Allow the hot-air gun to get up to heat{say 1 minute}before applying to IC. For more crowded boards make "conical" shrouds to surround the IC. I used some PTFE strip that i had but thin paxolin or similar but drilled and wired together would probably do. Cut 4 small trapezoids from the PTFE strip. Fixed together with all long edges one side and short edges adjascent on the other side. Fixed together with paper staples but for the smallest shroud for 8 pin SM had to wire together the final join. Forms a sort of truncated cone, frustrum, in shape. Tie to the PTFE cone (to stop the blower blowing it off) with copper wire or temporarily solder to distant points. When practised the heated contact time should be less than
2 seconds - no board distortion or collateral damage surprisingly. If you can't get the tugging wires under the IC then pass under a few pins at each corner. Because this tugging frees the IC at the earliest moment, the solder on the board is not fully melted and leaves a profile for localising the new IC in place and then solder pin by pin. SAFETY NOTE:- ensure good ventilation, use safety goggles,and beware of very slight risk of combustion.other hints and tips on
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
And for those of us without broadband, an outline of that method is ?
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Hope you've got a single-sided, single layer PCB, put the flat side on an upside-down hot iron, remove SMD's (all of them 'cuz they all melt) from board. Doesn't go into replacement of said parts.
so a no-no , i take it
Hi!
Probably a site of questionable reputation...I see a sign of the video and then get redirected promptly to a "DMV lemon law" page or something.
William
do it the RIGHT way and either
(a). throw it out & buy a new one.
(b). get a PACE or Weller hot gas bonder/debonder tool/station and do it the way the manufacturer (and repair depot) would.
All these methods are half ass "poor man" approaches that might work, but it's highly dependent on your skill level (and if you have to ask how to remove an SMT chip, you don't have the skill level).
the other question is, if you have no desoldering experience whatsoever - what kind of hands on electronics troubleshooting have you done to arrive at the conclusion that particular chip needs replacement ?
Go look on E-bay and you'll find many hot gas debonding tools to rework SMT boards.
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