Breaking the epoxy bond under SMD ?

I have successfuly used ChipQuik to free up the solder connections and then applying a bit of heat to the transistor itself with a little prying with a screwdriver. The heat helps loosen the epoxy a bit allowing the removal.

Dan

"In this case, the SMD was a one-ampere-capacity transistor.

"I wedged a scalpel tip (a needle point might work, too) under the device. I then touched a soldering iron to the pins, expecting that unsoldering them would allow the chip to pop loose. Apparently, though, the epoxy had been applied to keep the transistor forever in place, rather than just long enough for the initial soldering. I ended up breaking the transistor, while the epoxy remained intact.

"Any advice for next time?"

I'm biting my tongue.

"if relevant red colour and more than a micro-dot must have been under it as traces splurged out all around the body."

I can only make the vaguest of guesses as to what Mr Cook was trying to get at.

here,

relieve

free.

resolute.

micro-dot

then applying a bit of heat to the transistor itself with a little prying with a screwdriver. The heat helps loosen the epoxy a bit allowing the removal.

Your mention of screwdriver - I'd forgotten about my jeweller's finest screwdriver with the blade I'd ground angles, either side , to give close to a point. Insert under and twist 1/4 of a turn. I'd only used it under ICs before, where there is a bit more space , out to the pins. Have to check my drawer of ancillary "tools & kit" to check its still there and more importantly remember to try it next time

Hey William, I've found something that I think is just for you.

Here it is:

I'm sure they are lovely people, and you will have a whale of a time.

I'm guessing you were some kind of teacher, or Headmaster even, in your darker, younger days. Perhaps its time to let go of all that now, and embrace something a little more worthwhile.

Namaste.

I'm trying to help the guy. You're tolerating his lack of skill. Who's doing "something ... worthwhile"?

William, you do not seem to have a clue about what it is to be somebody other than yourself.

It's not too late to learn.

Gareth.

Mr.Cooks original post was a little confusing, not like his normal posts, and Mr Sommerweck is normally quite lucid, so he is not quite as bad a person as you have implied.

That may be so, but I am not basing my posts on this single thread.

Rather, it is based upon an observation of Mr. Sommerweck's recent history of posting on Usenet.

And this thread is typical of such recent postings, and, IMHO, shows little understanding of the Human Race.

Gareth.

One watt is a lot of power to be dissipating without a heat sink. May I suggest the epoxy is a heat conducting formula and was there to conduct the heat to the circuit board material.

Current designs use a device with a metal back side soldered to a large pad on the circuit board.

Paul

You're absolutely right. If someone has a problem, they ought to work to overcome it.

If you'd like to take this off line, I'd be happy to continue the discussion, in a friendly, constructive manner.

The issue is not whether I'm a bad person (I am), but whether anyone should publicly criticize someone who writes so poorly. I think they should, especially when a counter-example is provided.

William, you are still seeing them as being you.

They are not you, they are somebody else.

You have to try and imagine that possibility.

Gareth.

Because what you really want to say is ... ??

Why are you having to guess at anything, William ? For once, I thought it was quite clear that he was trying to remove the bloody thing from the board to replace it with a new one. Obviously, you don't get involved too much with surface mount reworks, as this is actually quite a common problem.

Arfa

a little LN usually works :)

Jamie

"Arfa Daily" wrote in news:OE6Hr.647752$ snipped-for-privacy@fx17.am:

I'm still trying to figure out why epoxy was used to hold a SMD on the board? thermal-conductive epoxy?

I also can't see epoxy having that tight a grip on the PCB,that it wouldn't break loose before the SMD package broke. must be some damn good epoxy,wish I knew who makes it and where to get it!

You were apply my final remark to the whole post, rather than to the text that immediately preceded it. If you look at my rewrite, it's obvious that I understood /exactly/ what I was trying to do.

That must be it, because it would have been "overkill" simply to hold it in place during the intial soldering.

(...)

I guess it's too much trouble to supply a usable clue as to what the device looks like. If it has a plastic or metal back makes a big difference here. Also, please make an effort to write in complete sentences that do not require cryptographic decoding.

Nobody uses epoxy to mount SOT transistors in a production environment. That's because it takes too long for it to set, and because it crumbles nicely when hot and softens exposed to alcohols and solvents. Single part epoxy has to be refridgerated in storage, making use on the production line somewhat awkward. Two part mixes hard quicker, but have a finite work time. Epoxies (and silicon rubber compounds) are used to attach physically large components, but not tiny SOT parts.

More common is cynoacrylate adhesives (aka super-glue) or attaching components before soldering. If the back of the xsistor is metal, it gets smeared with solder paste, which acts as a temporary glue, and then gets reflowed when run through the hot air soldering machinery. That solders the metal back of the SOT to the PCB.

wouldn't

epoxy,wish

Belt and braces , to take the mechanical strain off the solder? To scrape back the epoxy to a clean board , the action of a soldering iron tip on it, was like the normal reaction of solder-iron heat to epoxy, goes powdery . Perhaps its bright red as a warning