Idea for removing potting compound

[Whorse]

This is a really small thing, but I'm working on one right now. I don't have a toothbrush to sharpen, so had to comprimise.

Used a small exacto blade and started slicing 'layers' off the top. This was a reman board but the chip I want hasn't been cut out, so doing that (practice board mostly). When I got to the bottom nearly to the traces, I needed something that wouldn't damage the traces.

I grabbed a medium sized tie wrap/zap strap/cable tie/whatever you call it, and cut it so the weak end was gone and had a nice flush sharp edge on it. Seems to be working well for removing this stuff. Just a thought. I'm going to see what chemicals we have at work for removing this crap.

Is this stuff even epoxy? Seems silicone based.

[looneytuner]

Try soaking in acetone.

[Whorse]

gotta take it to work to get some

[87glhs232]

I don't have a toothbrush to sharpen, so had to comprimise.
.

You don't have a toothbrush?

I'm can't remember the chemical make up of that compound, but I do remember it's NASTY stuff. I wear gloves when handling them. If memory serves it had cyanide in it, or a compound that became cyanide when you melted it (ie. with your soldering iron). Be carefull!

[GLHNSLHT2]

a nylon/rubber brush on the dremel works great after cutting most of it off with my Swiss Army knife

[Whorse]

I'm not melting it right now. I did however find that isopropal with a toothbrush (that is rubber and can't be sharpened) and my zap strap is doing an amazing job. It's been less than an hour and I've almost entirely done both sides .I wouldn't hesitate to solder this, but I have time to clean it up nicer.

Update: Added a few photos. Before, During, and Now.

[cordes]

Nice work.

[Whorse]

Thanks! I've been reading your bit on the SBEC calibration. I think your writeups are excellent and a big help to people learning.

I am going to take this to work and hopefully remove the chip as is and keep it just in case. I'd like to see if we have any equivalent chips at work that might fit this, and I want to see what I might be able to order in for sockets.

I will see if we have anything that cleans this compound up any more.

[butchsuppe]

It,s almost impossible ( or maybe impossible ) to remove the chip in one peice since the potting glues it to the board. I,ve always used a dramel with a cutout whl. to cut the pins off the chip as close to the to top as possible. I don,t think you should use any chemical as it may damage the board, just my 2 cts. 1st board I did took 4 hrs, got it down to 2 hrs after doing 10. Buy a toothbrush to clean the board after the chip is removed. Good luck + enjoy the fruits of your labor.

[Tony Hanna]

Not to hijack your thread Jason, but does anybody make a remote socket/ribbon cable setup that a person could use to to mount the chip externally? I'm cleaning the potting on one myself (if I can find the box it's packed away in) and figured it'd be neat to do an external socket mounted inside a project case for easy access when swapping chips.

[sdac guy]

I use a small wooden stick that was made for electronic probing where non conductive nature is important. Then I use the business end of an old toothbrush to clear most of the crumbs, then I hit it with compressed air from a can (holding the board over a wastebasket to catch the crumbs).

Do not ever use any chemical to disolve the compound. The fumes from the compound in liquid form are extremely toxic.

Una has a very good process posted on his site (I don't recall the link) for doing the SMEC/SBEC's including many pics of progress along the way.

He mentions using side cutters to cut the pins on the chip and that is what I do. There is no metal dust doing it that way as there is when using a dremel to cut them. Probably takes a little longer than the dremel though.

Barry

[ShelGame]

Not to hijack your thread Jason, but does anybody make a remote socket/ribbon cable setup that a person could use to to mount the chip externally? I'm cleaning the potting on one now myself and figured it'd be neat to do an external socket mounted inside a project case for easy access when swapping chips.

www.moates.net

He has a lot of really cool stuff that we could use...

[87glhs232]

It's almost impossible ( or maybe impossible ) to remove the chip in one peice

Butch- I have to disagree with you there. True the compound is under the chip as well, but I have NEVER had to cut the pins. Last one I did was for mech1nxh, he didn't want a custom cal, but rather verify what the cal on it was (thought it was a mexican cal). I pulled the chip, read it, socketed the board and popped the chip in the socket then water proofed it. But to each his own. I'm sure it's a lot easier to cut the chip out and deal with the remains.

[sdac guy]

Butch- I have to disagree with you there. True the compound is under the chip as well, but I have NEVER had to cut the pins. Last one I did was for mech1nxh, he didn't want a custom cal, but rather verify what the cal on it was (thought it was a mexican cal). I pulled the chip, read it, socketed the board and popped the chip in the socket then water proofed it. But to each his own. I'm sure it's a lot easier to cut the chip out and deal with the remains.

I agree that I've never had a broken chip as long as all the pins have had 90% or more of the solder removed.

I cut the pins so there is much less chance of ruining the hole or solder trace near it by overheating it trying to remove the solder.

Cutting the pins, removing the chip, then removing the pins with a soldering iron, and then sucking the solder from the hole is far easier than trying to get all the solder out with the chip and pins in place. New chips are cheap enough.

Barry

[Tony Hanna]

www.moates.net

He has a lot of really cool stuff that we could use...

Nice site!
Looks like the EMUC 2818 cable combined with the HDR1 memcal header would work.
Thanks Rob!

[butchsuppe]

Nice site!
Looks like the EMUC 2818 cable combined with the HDR1 memcal header would work.
Thanks Rob!

If you build this let us know how it works, I think you got a good idea there.

[Tony Hanna]

If you build this let us know how it works, I think you got a good idea there.

If/when I build it, I'll start a thread with all the details and pics.
It's only $20 for the parts to do it, so if it tanks, I won't be out much.
I think I'm getting ahead of myself though. I haven't even got the potting cleaned off a board yet. I started, but it got boxed up when I moved and now I can't find the box. This was just an idea that hit me while I was considering what a pain it's going to be to remove and disassemble the smec every time I want to change the cal. I figure I'll be doing that pretty often as I learn.

[Whorse]

Which parts are you adding exactly? I have a board here with the potting compound all removed that I could try on and see if it works?

On a different note, I'm looking at a 90s TBI SBEC and a 91 Turbo SBEC. TBI has one less heat sink on it. Anyone know the physical differences?

[Tony Hanna]

Which parts are you adding exactly? I have a board here with the potting compound all removed that I could try on and see if it works?

The first pic is the ribbon cable (EMUC2818) from the Moates link Rob posted.
The second pic is the memcal header (HDR1) also from Moates.

The idea is to plug the ribbon cable into the socket on the smec/sbec on one end and the connector on the header on the other end. Then plug your eprom into the socket on the header. If it would work, it would allow you to mount the eprom externally (I was thinking of a small project case velcroed to the side of the smec/sbec) for easy access.

If you decide to try this, keep in mind that it's definately not a sure thing and may turn out to be $20 + shipping down the drain. I don't know what (if any) effect the length of the ribbon cable would have, and I'm not entirely sure what kind of socket is on the other side of the header since that's the only picture. That could be fixed easy enough with a zif socket though.
I'm curious to see if it'll work, but it'll be awhile before I'm ready to try it.

[sdac guy]

... On a different note, I'm looking at a 90s TBI SBEC and a 91 Turbo SBEC. TBI has one less heat sink on it. Anyone know the physical differences?

The TBI engine doesn't have as many injectors (only at the throttle body) as a turbo car (4-MPI) so the SBEC for the TBI will not work on a turbo car without heavy modification. That's why it has only one heat sink.

Barry