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How to desolder DRAMs from a large PCB?

tipc

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Here thinking back to the days when I actually wanted to repair a board, and nothing but a Radio Shack soldering iron and solder wick were nearby. No propane or blow torches, noskillets, hair dryers or heat guns. No peanut oil. No buckets in which chips would accumulate. No lineman's pliers. No hacksaws. But I'm learning a lot. Please continue :)
 

Chuck(G)

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No, they just can clear a hole where a sewing needle used to be used. They're hollow, so you can get them around a pin or wire and isolate it from the via/pad. Cheap and very handy--solder doesn't stick because they're stainless.
 

Dwight Elvey

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For an alternate method. You take a 2x4 and drill about a 1 inch hole in it. Hold the board about a foot over the 2x4 with the pins down. Warm the solder from the top. When you believe it is good and hot, slam the board down, flat, onto the 2x4 over the hole. I've don't this method when desperate and away from my bench.
Dwight
 

Theodric

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Another option not yet presented is a low-melting-temperature desoldering agent like Chip Quik. It's good for particularly stubborn chips with lots of pins, or stuff like regulators and SMD bricks where the solder goes underneath, out of reach of your wick or the Hakko's suction.

Use a normal temperature on your iron, like 350ºC. You put down some of the delicious-smelling flux, then lay down a bead of the solder bridging all pins on the IC. The low melt temp and normal iron temp allow it to remain molten for longer, giving you time to work the part loose.

It's not cheap, but sometimes it's cheaper than what you're trying to salvage.
 

Chuck(G)

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"Low temperature fusible alloy" -- I've mentioned it for a few years. I've used it to safely remove a specific surface-mount component, say a TQFP from a populated board, while leaving the rest of the board intact. In my case, I simply took some of the filler metal I use to bend thinwall tubing--Cerrobend 158 (158F is the melting temperature of the stuff), powdered some of it (using a file) and tucked the powder around the pins that I wanted to free. No soldering iron necessary--I simply used an ordinary 150 watt PAR spotlight on the area. The alloy melts, dissolves the solder and the part slides right off. Cleanup with a toothbrush. A hot air soldering tool set low would do the same.

Wood's metal slugs are far less expensive than the stuff that Chip-Quik sells. A quick look on eBay shows a 4 ounce stick for $10 shipped. Be aware that technically, these are hazmat, as they contain cadmium and lead--so dispose of safely.
 

maxtherabbit

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For an alternate method. You take a 2x4 and drill about a 1 inch hole in it. Hold the board about a foot over the 2x4 with the pins down. Warm the solder from the top. When you believe it is good and hot, slam the board down, flat, onto the 2x4 over the hole. I've don't this method when desperate and away from my bench.
Dwight

Love it, impact extraction
 

GiGaBiTe

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"Low temperature fusible alloy" -- I've mentioned it for a few years. I've used it to safely remove a specific surface-mount component, say a TQFP from a populated board, while leaving the rest of the board intact. In my case, I simply took some of the filler metal I use to bend thinwall tubing--Cerrobend 158 (158F is the melting temperature of the stuff), powdered some of it (using a file) and tucked the powder around the pins that I wanted to free. No soldering iron necessary--I simply used an ordinary 150 watt PAR spotlight on the area. The alloy melts, dissolves the solder and the part slides right off. Cleanup with a toothbrush. A hot air soldering tool set low would do the same.

Wood's metal slugs are far less expensive than the stuff that Chip-Quik sells. A quick look on eBay shows a 4 ounce stick for $10 shipped. Be aware that technically, these are hazmat, as they contain cadmium and lead--so dispose of safely.

I'm going to have to try this. I've been looking for a way to put less heat stress on PCBs for awhile now, but there's no way I was going to pay the insane amount of money they want for chip quik.

A single brick of the Cerrobend is so much cheaper. The cadmium is obviously not great, but already dealing with lead and other heavy metals when soldering so it's not a big deal.
 

glitch

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Started with the torch, graduated to heat gun. I was super good with a torch, I didn't have a temperature-controlled iron until near the end of college, so I'd recap P4 motherboards and iMac G5 machines using the propane torch for desoldering and preheating on soldering in the new caps.

I typically would put the board in the bench vise, work the solder side with the torch, and pluck the chips out with either needle nose pliers (small stuff) or tongue-and-groove/channel lock pliers. Drop them into a metal coffee can or similar non-meltable container.

As mentioned, do it outside or in the garage with a fan or something :p
 

DeltaDon

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You can also find some low melt lead free solder paste in a syringe that is much cheaper than the Chip Quik low melt solder. Often found on eBay for under $10 for 30 to 50 grams.It also uses bismuth as the means of lowering the melting point. I needed some of this stuff for a nasty memory board out of a mini or main frame computer with some no lead solder that I think melted at 5 million degrees. Or so it seemed. It had inner layers of copper for power and ground that absorbed heat. The worst board I've even seen for desoldering. It might have been the fact that the board had gone through a fire and some of the glass fibers in the board were not only visible but fraying. It held about 128 4116's and I really wanted them and so I worked at finding a solution that didn't cost more than the value of the chips. A few had their markings missing caused by the flames or heat, but still tested A-OK and are still working.

I also have an Ungar (I think that's the brand) device I picked up some 30-40 years ago that is a spring loaded device with two fingers that slip under the ends of an IC and apply pressure while you heat from the solder side. It works well if the chips aren't flat against the board. I haven't seen one of this for sale in a gazillion years. It didn't help with the above board since the IC's were against the board and the fingers won't fit under them. There was a second type that worked on round TO-5 can devices too.

The method suggested by Chuck of wacking the a board against the work bench works great and I've used it for years. This method is also great for opening solder filled holes for through hole components that just seem to defy normal solder sucking. I did learn never to wear shorts and wack directly over an exposed leg. :crazy:
 
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