Removing 14 pin DIL devices from double sided populated PCB's? - Page 1
Forum section: electronics / beginners

author: Chris Wilson
author_rank: Super Contributor
timestamp: June 10, 2014, 12:04:22 pm
content: I removed a 14 pin Op amp from a double sided, populated used PCB by cropping the pins along the sides of the device and removing each one individually with low thermal mass, (fine tipped), pliers and an ordinary Pace soldering station / iron. I tried with the device intact with my Pace vacuum de-soldering tool, but was not successful in removing solder from the device side of the pins with what I thought a reasonable amount of time putting heat into the pin from the reverse side. I fitted a socket once the device was out!Are there better ways? An acquaintance uses a heat gun, but I am unsure whether he is talking paint stripper size, or a dedicated device that heats small, controlled regions.How do the professionals do it? How do *YOU* do it?Thanks.

author: rob77
author_rank: Super Contributor
timestamp: June 10, 2014, 12:17:12 pm
content: the best is to use hot air - but not the paint stripper. there are dedicated hot air stations for such a purpose (the cheapo chineese ones start at 60-70Eur).actually the paint stripper hot air gun is usable as well - but more for part recovery when you desoldering everything from the board.

author: TheWelly888
author_rank: Frequent Contributor
timestamp: June 10, 2014, 12:17:12 pm
content: The best tool to remove DIL ICs from double sided boards are desoldering tools, they have heated tubes and vacuum is applied to remove the molten solder. Even so, they are not that easy to use! What I do is to make sure BOTH the underside pad and the IC pin are heated (at 370 deg C) at the same time and allow heat to conduct through the hole plating before applying vacuum. Usually the solder all comes off and wiggle the IC pin beofre removing heat in order to break any residual solder.Any that doesn't take, resolder the joint with flux and try again before the the joint cools down.I admit that even with practice, I have had to snip pins off then desolder.

author: mazurov
author_rank: Frequent Contributor
timestamp: June 10, 2014, 04:00:21 pm
content: Quote from: Chris Wilson on June 10, 2014, 12:04:22 pmIf your goal is to save the board the best method is the one you're using. Use tweezers instead of pliers to better feel when the solder becomes liquid and it's time to pull the pin out.I remember those old ceramic DIP-ish packages where you couldn't cut the pin off the side with the pliers but had to pry them one by one.I do the same thing leaving 2 diagonal pins (like pin 1 and 8 on 14 pin DIP) attached to the package.

author: retrolefty
author_rank: Super Contributor
timestamp: June 10, 2014, 04:07:07 pm
content: In the mid 70s I was a field engineer for service on mini-computer systems. Our main PCBs were 4 layer where the ground and power planes were inner layers making removing and cleaning the power and ground pins nearly impossible in the field. What we did is cut out the bad DIP and tack solder the new one onto the stubs. Looked like hell, but worked great and I never damaged a board using that method.

author: SeanB
author_rank: Super Contributor
timestamp: June 10, 2014, 05:05:08 pm
content: Did similar on avionics boards, where you could not get to the bottom set of leads as there was a package in the way on the other side. Snip the leads off, and then polish the inner side to bare base metal and solder the new chip to the stubs using stubby leads. The boards were made by applying solder paste to the holes, then placing the 400 odd dip packages to the 20cm by 15cm board on both sides then doing a vapour phase reflow of the whole board. No way to repair other than by that method, as they were regarded as basically throw away items, with a price tag that was about the equal of that mass of Platinum. All 0.1 in parts, and spaced at 0.1 inch on both top and bottom, along with being a 16 layer board with a few power and ground planes, as there were 2 5v rails per board. Most of the time fixing a fault was by playing mix-n-match to get a set of boards which would time with each other reliably over temperature. If wrong it would fail when cold and work when hot, or do it the other way around.

author: Chris Wilson
author_rank: Super Contributor
timestamp: June 10, 2014, 06:04:51 pm
content: Glad I asked, some great info here! Also glad snipping the leads was the right way to go. the board is precious, the op amps pence.... What's a good hot air pencil, or whatever device is good to use hot air to remove things? I have been very happy with my Pace vacuum de-soldering iron, but it was defeated in this instance. This is a great forum, far better than most that are UK based, the breadth of knowledge is humbling, as is the willingness to draft detailed posts.

author: rob77
author_rank: Super Contributor
timestamp: June 10, 2014, 07:19:20 pm
content: Quote from: retrolefty on June 10, 2014, 04:07:07 pmit reminds me of the old days (early 90's) when i was repairing a few 8bit home computers (local zx spectrum clones) - lot of cases with all DRAM chips gone because of reversed 5 & 12 V (lot of guys were trying to repair a broken power cord , but soldering back the 5V & 12V reversedsurprisingly the German Z80 clone and Russian ULA clones were surviving without any issues)i used the very same technique to replace the dram chips - cut off the old ones - shorten the pins on the new ones and solder them in place- guaranteed success with no damage to the PCB

author: woodchips
author_rank: Frequent Contributor
timestamp: June 11, 2014, 08:39:39 am
content: I have always found that hot air just doesn't work, no thermal mass to raise and keep the temperature above the solder melting point. To compensate you wind the air temperature up and up and then have a delaminated PCB.I bought one of the cheap Chinese solder pots on ebay, about 60mm diameter, brilliant. They would be even better if the flange around the outside diameter was cut away so the edge of the pot was a simple thickness of the stainless pot. These pots, even at only 200C, have more than enough thermal mass to unsolder anything almost instantly, even PGA devices.Well worth the silly money they cost.

author: madires
author_rank: Super Contributor
timestamp: June 11, 2014, 09:14:14 am
content: AFAIK Weller offers some special desoldering tips for DILs. That reminds me of my SMT desoldering tweezers. Haven't tried to use the SOIC desoldering tips for DILs yet.

author: tautech
author_rank: Super Contributor
timestamp: June 11, 2014, 09:56:56 am
content: Quote from: Chris Wilson on June 10, 2014, 12:04:22 pmIn the good ol days when there wasn't the PCB density, holes and pads were of a generous size and you could reliably remove an IC AND use them again!These days, what you have done is perfectly acceptable practice and often your only option.Often one has to resolder, desolder stubborn pins to get them clean, and I keep a spool of low temp quality solder just to mix/dilute some of the horrible brews that manufacturers use.

author: david77
author_rank: Frequent Contributor
timestamp: June 11, 2014, 10:33:37 am
content: I find it always depends on the board you're working on, sometimes I have great success with only solder wick and sometimes I need to fix the board vertically on the bench to apply a soldering iron from the component side and use the vacuum iron on the other side.Snipping the pins and pulling them out one by one is also a valid technique, probably one of the more gentle methods one can use without special tools.Also on some boards it is much easier to accidentaly lift traces then on others, I've had problems with Philips consumer stuff from the late 70ies, the traces would literally fall of the board as soon as they saw a hot iron.

author: KJDS
author_rank: Super Contributor
timestamp: June 11, 2014, 11:17:13 am
content: Metcal do this tip, an SMTC-162 for their irons.Generally I use hot air, but I've got a lovely little Leister unit that you can keep the air temp low enough not to scorch the board but high enough to quickly melt solder. I've had less success with cheaper heat guns, but that may be due to lack of patience.

author: SeanB
author_rank: Super Contributor
timestamp: June 11, 2014, 05:41:08 pm
content: I did buy the Weller flatpack tip, and it was $80 ( in 1990) but it was a great time saver on those horrid packages on the world's flakiest boards that they were placed on. I wanted the IC off and the tracks saved. I hated having to stick them back down and then solder the new one on top of them.

author: rob77
author_rank: Super Contributor
timestamp: June 11, 2014, 08:45:28 pm
content: Quote from: woodchips on June 11, 2014, 08:39:39 amthen you must be doing something terribly wrong.. either your hot air gear is rubbish or your procedure.i'm doing it this way:1. heat up the board to cca 120-180 celsius with hot air (to avoid warping of the PCB)2. crank up the hot air to 250-300 celsius3. melt the solder joints of your part4. take out the part from the board (or let gravity do the job)i never burned a single PCB this way. you can even desolder a PCI bus connector or CPU socket using this method.

author: Chris Wilson
author_rank: Super Contributor
timestamp: June 11, 2014, 09:07:04 pm
content: With a double sided board with a DIL connected to both sides, do you use the hot air on just one side, or both?

author: rob77
author_rank: Super Contributor
timestamp: June 11, 2014, 09:30:08 pm
content: Quote from: Chris Wilson on June 11, 2014, 09:07:04 pmone side - for DIL/DIP the bottom side. (or any other through hole parts)for SMT - the "top" side (heating the components during de-soldering)if the board has more layers and inner ground/power planes, then the preheat needs to be longer (but not higher temperature) to ensure the inner layers are preheated as well and the board will not warp.if salvaging everything from a board - then again bottom (regardless of through hole or SMT) - but in that case (you don't care about the PCB) i'm not using my hot-air station but a mighty paint-stripper hot-air gun set to approx 300 celsius. with a brief pre-heat (just blowing from a bigger distance for pre-heat).