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IBMMuseum
December 29th, 2011, 11:26 AM
Looks like an appropriate posting location...

I've been harvesting parts from non-functional clone motherboards, and wonder about some of the nuances others may use:

Typically I localize the heatgun on the solder side, then rap the board down over a cardboard box. Excess solder splashes in thin coatings over the surface of the components, although it can usually be etched or wiped away. I might try over a bucket of water, in the hope that the solder drops would be separated from the components, hardening before it "splashed" on them.

Thoughts?...

barythrin
December 29th, 2011, 12:16 PM
I've always used a desoldering iron which goes over each pin to melt the solder then generally I pull the component off myself. A heat gun sounds like a much easier way to do it other than the symptom you're referring to. I would stick to pulling the component off vs banging it on something just to prevent that splashing. That or possibly put the board on it's side so it drips down vs onto the package, etc. I know some folks heat it up from the component side or use that soldering flux stuff. With the heat I'm not sure how likely it is to damage the parts.

gubbish
December 29th, 2011, 12:55 PM
I also use a desoldering tool that goes over the pins as, and find that it works pretty well. Some pins are troublesome, and for those the trick is to add a little bit of new solder to the joint. Somehow after you do that the desoldering tool sucks it right up. It's important to keep the tip of the desoldering tool clean so the suction happens quickly when you release the bulb. Also make sure you squirt out the removed solder somewhere before putting the tool back over the board, since you can spray solder everywhere if you forget.

Chuck(G)
December 29th, 2011, 01:06 PM
Before I used the heat-gun approach, I used a propane torch (outdoors)--stank to high heaven. Either one is only useful for harvesting gross parts--small SMT stuff generally requires a more refined approach. If it's a fine-pitch SMT item, I'll use a hot air pencil.

I don't worry about the solder blobs; usually they can be knocked off with the end of an X-acto knife.

IBMMuseum
December 29th, 2011, 08:06 PM
I've also heated up the solder-side, then rap it on that side to get a little more of the excess solder. Really, for those that haven't tried it (I've also done the propane torch), the speed which you can work through boards is pretty good (my heatgun is a nice Milwaukee unit). As long as you are careful the heat won't damage components.

I'll try into a bucket of water and see what it does (although the sudden heat change might be bad for the chips I am trying to harvest)...

Chuck(G)
December 29th, 2011, 08:24 PM
I'll try into a bucket of water and see what it does (although the sudden heat change might be bad for the chips I am trying to harvest)...

I'd be afraid of that also.

I've also known people to strip boards by putting them in an electric skillet filled with peanut oil. Heat to about 380F/190C. Since 63/37 Sn/Pb solder melts at 188C/370F, the oil bath will liquefy all solder without burning the components. Wear eye and skin protection--hot oil is nasty, although the oil temps used for deep-frying are generally higher.

For delicate SMT ICs, I use Wood's Metal powder to lower the melting point down to about 170F, where it can be melted by an ordinary PAR38 spot. Clean-up is easy and it preserves the PCB traces. WM contains cadmium, so don't breathe the fumes. Dispose of responsibly.

Maverick1978
December 30th, 2011, 01:00 PM
I've seen where people use clothes irons to melt the solder and lift the components off... I'd be rather scared to do that. Right now, there's not alot that I need for the parts bin, so I tend to just hold onto the populated board(s) and desolder components individually as needed.

That heat gun method looks nice though - I've seen vids of guys harvesting parts with those before... MAN!

Chromedome45
December 30th, 2011, 05:27 PM
I guess I am old school. Iron & solder sucker for me.

ibmapc
December 30th, 2011, 06:56 PM
For delicate SMT ICs, I use Wood's Metal powder to lower the melting point down to about 170F, where it can be melted by an ordinary PAR38 spot. Clean-up is easy and it preserves the PCB traces. WM contains cadmium, so don't breathe the fumes. Dispose of responsibly.

Have you considered using a non toxic alternative to Woods Metal? I believe Fields metal has a simalar melting point and does not produce toxic gasses

Druid6900
December 30th, 2011, 06:58 PM
I use the paint scraping type of hot air gun approach too, but, I use a couple of saw horses with a box that is about 3 ft x 1 foot so I can do several boards at the same time going back and forth across all the boards. A regular tap with the heat gun in the area I'm working on dislodges the chips and they drop into the box.

This setup allows the solder, which has to fall further, to harden before it hits components in the box.

I routered a channel in the 2 x 4s at the top of the saw horses to set the board upright and use that part of the setup to harvest the SMT parts in the same manner, but with the boards being held vertically.

Just keep the gun moving at a constant speed and you won't damage the chips.

Chuck(G)
December 31st, 2011, 12:43 PM
Have you considered using a non toxic alternative to Woods Metal? I believe Fields metal has a simalar melting point and does not produce toxic gasses

I'll give it a try when I run across some. At a high temp of less than 200F, I'm not sure how much in the way of toxic gas would arise from either, however. I've got pounds and pounds of the Woods stuff, however.

RJBJR
December 31st, 2011, 01:34 PM
I accidently "harvested" the components from a MCMaster when I let it get too hot in the oven and tipped it sideways when pulling from the oven. I mention this only because I don't see any mention of the oven as a tool for harvesting.

Chuck(G)
December 31st, 2011, 03:06 PM
I've used a toaster-oven for smaller boards. For larger ones, a convection oven might be better. You need one with good temperature control, otherwise soft plastic such as connectors can suffer badly.

If you have a DMM with a temperature scale and a K-type thermocouple, you can use it to monitor the temperature.