Take off circuit sotp memory 54 pins

[GGMM]

hello,

I have to unsolder memory circuits sotp 54 pins.
1) The weld does not appear to melt with the hot air and flow. Even when testing at a maximum of 450c° from my station.
2) I feel that these circuits are glued, do you have a method to remove this glue before release.
3) I tried to put weld  on one side and try to unsolder with iron.  Badresults of pads are unstuck.   >>>so stop before more all destroy!!!
Anyway, a real mess...

some ideas?

[Audiorepair]

Cut through all the legs with a sharp blade.

Then carefully remove all the legs with a soldering iron.

Then deal with removing the IC body left behind.


Dave shows how here:

[wraper]

If it really glued, you can melt solder with hot air. Then while continuing heating, hold IC with pliers and twist it little bit clockwise/counterclockwise, back and forth until glue gives up. If solder does not melt, it has nothing to do with glue. Maybe PCB has many layers and sinks heat away too well. Then you may need hot air with higher airflow and preheater under PCB.

[GGMM]

Thank's for you answers.

I’ll wait a little before I do anything and make it worse.
I ordered a microscope on A.... X, we’ll see better than my mole eyes. lol
Yes I tried with a cutter to cut the legs, but I didn’t get the expected result, because it slides on the lower legs.
For the glue, I will see once all the legs are cut off.
cdt

[Bud]

If your PCB is a multilayer one with ground plane and power planes, it may be difficult to unsolder components with just heating them from above. You may need to pre-heat the PCB by placing it on some sort of heat plate that will heat it from below to 100-150C. Then use the hot air pencil to unsolder a particular component.

[Audiorepair]

Thats why cutting the legs off can be a really good idea.

[GGMM]

Bud,

I can’t heat the PCB at the same time on the other side of the board, because there are 2 very large components that are welded from below.
see picture
I don’t want to make things worse.
Before I touched the memories, I tried to heat the flat in case a weld failed.
It’s very common on PS2 consoles, I fixed it like this.
But the error  remained.
cdt

[GGMM]

hello,

Do you think that if the memory chip is glued on the pcb, that I can inject below it (By putting the pcb vertically so that it goes down on the whole circuit) a little bit of bomb-style degraising antgraffiti or brake cleaning with the small tube on the nozzle to remove the glue or at least lessen its effect?
Is that just an idea, if you have better?

cdt

[wraper]

99% chance it's not glued. And while you believe preheating is dangerous, it's exactly opposite. It's way more dangerous to solder this without preheating.

[GGMM]

Hello Wrapper,

There are red dots on the PCB (see picture before) , not necessarily on the chips. I read that if there are red dots, it is glued.(?)
In any case, the legs being cut on one side, I can not rock the circuit. Also the space between the 2 memories is so small that you can’t pass a tweezer, I try to weigh it with a small screwdriver without effect.

I don’t want to force.
 I have a one in four luck of bumping into the one that broke down. Could not watch the signals because the board is covered by the CPU board and all this in the box!
It’s at random

cdt

[wraper]

The only red dots I see look like marker ink, not adhesive.

[GGMM]

Wrapper,

See here for example:
https://www.reddit.com/r/AskElectronics/comments/7mtoy3/what_are_these_red_dots_on_this_pcb/

Since there are components on both sides, maybe on one side it was glued for flow?
I only see that as an explanation ?? But I’m not a flow specialist for the explanation and this is the first time I try to remove this type of circuit.
cdt

[wraper]

In most cases adhesive is not used for double side assembly. These RAM ICs can easily hold by solder surface tension while upside down. As of that example, it's a single layer board which was wave soldered, not reflowed. So SMT components need to be glued before soldering.

[GGMM]

Wrapper,

I didn’t quite understand your answer.
The board is actually multilayer with components on both sides.
On the other side is 2 flats whose connections are below (Like a processor, at least more than 100 connections)
On the other side are the memory's.
So, for soldering the card was can be laid flat from the top and memoires below so glued?? It is a mortgage.
In any case, even at 450C it didn’t seem to melt. Yet I trained on various techniques and in hot air I had no worries. (See example with memory pcb PC)
cdt

[wraper]

That memory PCB has no thermal mass to sink the heat away. Try modern high-end graphics card, you will be barely able to desolder anything without preheating no matter how powerful your hot air is.

[wraper]

Also for these you could simply get low melting point alloy like chipquik or similar.

[wraper]

So, for soldering the card was can be laid flat from the top and memoires below so glued?? It is a mortgage.

No, they will not fall off even when solder melts. The trick is to solder all of heavy components (compared to pad area) on second pass. You have shown a RAM module as example. Is it double sided? Have you seen any glue on either side?

[wraper]

[GGMM]

I have melting paste at 138C°  and flux, but I didn’t want to use it to solder.
Can be tried (?)
I didn’t want to do that in the first place, because I feel like the PCB is not getting dirty anymore.
we’ll see I’ll test


thank's for your help

[GGMM]

you’re right, no glue on ram PC. Thank's

[wraper]

I have melting paste at 138C°  and flux, but I didn’t want to use it to solder.
Can be tried (?)

You can apply it for easier component removal. Then clean the pads using normal solder.

[GGMM]

Hello,

I received my set of 5 precision clamps from A...N. Less than 12€.
As said before, I tried to grind to have as little space as possible to cut the legs of a sot chip memory 54 legs.
The space is very small less than 0.5mm, but I admit that my test on my ram PC  is conclusive. Must be fairly precise when grinding. The advantage of having five is that we can catch up.
Nb: The picture is misleading, it’s thinner than in trade
cdt

[GGMM]

hi,

That’s the day I tested my precision clamp that I filed.
Frankly, less than a minute to cut the 27 legs on one side. I wonder why I haven’t tested this method before.
The hot air gave me nothing, and the cutter damaged me more than 4 tracks that can be seen in this picture.
To Wraper, I would say that there is a glue under the circuits. This one is soft but sufficient to hold the circuit. Maybe the hot one softened it, but the circuit board comes off easily.
So in the picture, you will see a location (a little damaged but recoverable), where the residues are desoldered. A other location, where the cut legs and the folded legs are visible before desoldering.
For the repair of the 4 tracks, a small wire will do the trick, I even saw that some take off pads on old PCB to correct.
That’s the day I tested my precision clamp that I filed.
Frankly, less than a minute to cut the 27 legs on one side. I wonder why I haven’t tested this method before.
The hot air gave me nothing, and the cutter damaged me more than 4 tracks that can be seen in this photo.
To wrap, I would say that there is a glue under the circuits. This one is soft but sufficient to hold the circuit. Maybe the hot one softened it, but the circuit board comes off easily.
So in the photo, you will see a location (a little damaged but recoverable), where the residues are desoldered.A location, where the cut legs and the folded legs are visible before desoldering.
For the repair of the 4 tracks, a small wire will do the trick, I even saw that some take off pads on old cards to correct.
cdt

[wraper]

To Wraper, I would say that there is a glue under the circuits. This one is soft but sufficient to hold the circuit.

Looks like solidified flux left from your operations. It's not how SMT adhesive looks like or is applied.

[GGMM]

Hello Wraper,

Normally I only worked on one chip. But actually it can remain of the flow that sank from underneath?
We’ll see about the other two chips if we have to unsolder them.
The main thing is that the clamp method is really simple and effective. In 2 minutes the circuit is removed.
I should have tried before. LOL
cdt