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Breaking the epoxy bond under SMD ?

N

N_Cook

Transistors , in this case 1-amp-continuous "size" whatever the SO
designation of that is.
If I've not used hot air then a scalpel tip or needle point, as used here,
wedged under , soldering iron melt solder a touch leting the pins relieve
themselves away from the lands , repeat wedging/desolder until fully free.
But this time the epoxy was more structural than just for placement.
I ended up breaking up the transistor body and the epoxy stayed resolute.
Any advice for next time ? if relevant red colour and more than a micro-dot
must have been under it as traces splurged out all around the body.
 
W

William Sommerwerck

Transistors , in this case 1-amp-continuous "size" whatever the SO
designation of that is.
If I've not used hot air then a scalpel tip or needle point, as used here,
wedged under , soldering iron melt solder a touch leting the pins relieve
themselves away from the lands , repeat wedging/desolder until fully free.
But this time the epoxy was more structural than just for placement.
I ended up breaking up the transistor body and the epoxy stayed resolute.
Any advice for next time? if relevant red colour and more than a micro-dot
must have been under it as traces splurged out all around the body.

"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.
 
N

N_Cook

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.

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
 
W

William Sommerwerck

Hey William, I've found something that I think is just for you.
Here it is:
http://teachempathy.com/self-empathy/empathy-as-a-way-of-being-retreat/
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.

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

Paul Drahn

Transistors , in this case 1-amp-continuous "size" whatever the SO
designation of that is.
If I've not used hot air then a scalpel tip or needle point, as used here,
wedged under , soldering iron melt solder a touch leting the pins relieve
themselves away from the lands , repeat wedging/desolder until fully free.
But this time the epoxy was more structural than just for placement.
I ended up breaking up the transistor body and the epoxy stayed resolute.
Any advice for next time ? if relevant red colour and more than a micro-dot
must have been under it as traces splurged out all around the body.
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
 
W

William Sommerwerck

I'm trying to help the guy. You're tolerating his lack
William, you do not seem to have a clue about what
it is to be somebody other than yourself.

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.
 
W

William Sommerwerck

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.

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.
 
J

Jamie

Arfa said:
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
 
W

William Sommerwerck

Why are you having to guess at anything, William?

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.
 
W

William Sommerwerck

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

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

N_Cook

Jim Yanik said:
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!

--
Jim Yanik
jyanik
at
localnet
dot com


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
 
N

N_Cook

Jeff Liebermann said:
(...)

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.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com [email protected]
# http://www.LearnByDestroying.com AE6KS


The device was FZT949 (yes, revised, 5 or 6 amp rating/size) , the glue
cleared away with soldering iron tip , in the manner of epoxy , with no
smell of cyanoacrylate
 
W

William Sommerwerck

As ever, you've lost me there.

Yeah, everyone else got it. I understand why you misunderstood -- you
misread the context of the last statement.

I might say to all the professionals in this group -- how can you work and
respond to postings at the same time?
 
N

N_Cook

Jeff Liebermann said:
<http://www.diodes.com/datasheets/FZT9489.pdf>
SOT223 package.
<http://www.diodes.com/_files/product_packages/sot223-3l.gif>
Full spec dissipation requires 4 square inches of copper under the
device. Lower dissipation specs with less of a heat sink. The back
is the device is plastic. Most of the heat comes out the large solder
tab. There is a 1.6mm air gap under the plastic case to deal with
glues and to insure that the tab mechanically hits the copper head
sink area. There is almost no value in obtaining a thermal connection
to the epoxy case, so there would be no benefit to using a thermally
conductive epoxy glue.


Epoxy does not "clear away" when hit with a soldering iron. What it
does is crumble and burn leaving a charred mess. The heat conductive
variety will conduct enough heat to the PCB to also char the PCB. I
agree that if it didn't reek when you hit it with the soldering iron,
it's probably not cyanoacrylate adhesive. That leaves hot melt
adhesives and various acrylic glues. If it seemed to melt away at a
very low temperature, it's probably hot melt. If it took some effort,
and it simultaneously melted and charred slightly, it's acrylic.

Please specify what you mean by the "manner of epoxy"? Melt, char,
crumble, volatize, explode, etc?

--
Jeff Liebermann [email protected]
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558


Crumble without clumping or sticking and without a change of colour and no
observed smell given off.
 
W

William Sommerwerck

I might say to all the professionals in this group --
Well, William, I expect that's for us to know, and you
to "guess" at ... :)

I'm currently editing articles for "Electronic Design". The writing quality
varies from barely acceptable to horrible. I have to guess at a lot of
things -- such as what the writer /thought/ he was writing about, or what a
particular sentence Really Means. I often refer to Wikipedia or search the
Web, but sometimes it's a guessing game.

Do any of you know what an IBC is? I didn't, and couldn't find the answer
anywhere.
 
W

William Sommerwerck

I'm currently editing articles for "Electronic Design".
My compliments. I read the printed edition and find
the articles to generally quite acceptable.

Thank you. Did you like "Did you buffer the buffered buffer?". That was one
of my edits.

I'm not the only editor, of course. They have full-time writers and editors
who do a very good job.

I've scribbled a few articles in the distant past. I could almost
recognize my original article buried in the published version.

That suggests the original had significant problems. (I don't /know/, of
course.) I have carte blanche to completely rewrite articles if I think it
necessary. Many go through an extremely heavy edit -- and sometimes major
rearrangement -- which the authors generally tolerate. (I would /like/ to
think they look at the edited piece and accept it as a significant
improvement. The late Bob Pease didn't. He told me my edits didn't
contribute anything. That's about what Beethoven said about Haydn.)

In some cases I'm asked not to disturb the original style too much. I just
finished editing a piece about the advantages of custom analog ASICs, for
the purpose of not only cutting costs, but avoiding counterfeit devices. The
author had a fun, engaging style, which I didn't have to alter in the
process of cleaning up his writing (mostly correcting grammar errors and
tersifying here and there). Indeed, my edits actually pushed the piece
/closer/ to the original style.
However, those are minor compared to what the magazines do
to themselves. Authors are told to "not worry about style" and
just supply the facts and details. The magazine editors will take
care of making the article presentable. Permit me to offer some
praise and sympathy.

There are articles so bad I feel my skull is about to explode. (In one case,
the article was so awful and required so much time that I asked for a bit
extra, which I got.) But I keep telling myself that, if engineers could
write, I wouldn't have this job.

Insulated Bridge Clip. They're used on Type 66 telephone blocks.
They're usually bright red and indicate either a "protected" circuit
or one that can't be detected with a common butt-in.
Like this, but covered with red vinyl insulation:
http://www.ebay.com/itm/390400364255

That's not it. Not anything like it. Though it /is/ used in telecom systems,
on the block diagram an IBC is some type of regulator/isolator.
 
W

William Sommerwerck

Does Penton seperate the technical editing from
the grammar/spelling/style/fit editing? I had quite
a problem with that when doing several book edits.

Not as far as I know. But my boss was surprised at how heavily I edited one
piece, as it had been past another editor previously.
Do the original authors even see the results of all
this editing? I didn't see anything until the final print
version. However, times may have changed.

Apparently they do. One didn't understand why I had so heavily edited his
work, and I had to justify it. The article was published as I had edited it.

If Bob Pease's column in EDN were any indication of
his writing skills, I would ignore his comments. It's a
great collection of disconnected anecdotes and trivia,
but would not pass for much beyond a grade skool paper.

Bob's writing was readable and understandable, but it certainly isn't what I
would consider first-rate technical writing.
What editors do is make the content more accessible
to a wider range of audience. It's very difficult to write
something that is acceptable to both the experts and
beginners in a field.

Bingo! I was just saying that to my boss. You want to write so that people
who are simply /curious/ about the material can read and understand it.
That's exactly what I do. Poorly written jargon discourages readership --
and thus subscribership.

Nice. However, I suspect that was written by someone
involved in the marketing or sales of ASIC's and not an
engineer involved in design or production.

No, he's a major engineer of such. His name is Frosthold, and I wanted to
add this to his bio: "He has two brothers, Fasoldt and Fafner Frosthold, who
design and build custom homes."

A little context is always helpful.
Next guess is "Intermediate Bus Converter".
<http://electronicdesign.com/article/power/select-the-optimal-intermediate-b
us-converter>

That's it! Thanks! (I'll get my boss to add a cross-reference.)

By the way, it's rather wordy. It could stand another editing pass.

PS: I'm typing this on a Unicomp buckling-spring keyboard. It's the only way
to type.
 
W

William Sommerwerck

PS: I'm typing this on a Unicomp buckling-spring keyboard. It's the only
way to type.
<http://www.pckeyboard.com>
Bah... I constantly switch computah keyboards when I work on multiple
machines in my office, and when I use various machines at customers
locations. As long as the general layout is similar, it only takes me
a few seconds to adapt to a new keyboard. These vary from glass touch
screens (Android, iPad, etc), elastometric flat (industrial
controller), rubberized (restaurant kitchen), almost flat with minimal
travel (laptop), dome keys (cheap keyboard), X shaped wire (better
laptop keyboards), and antique teletype machines (brute force finger
exerciser). Keyboards that give me problems are laptops where the
keyboard layout is rearranged to provide room for the add keys which
are never used, and Apple "chiclet" keyboards, which jam on the sides
of the keys when dirty. If you're stuck on one keyboard style, I
suggest you try some others. You might learn to like them better.
<http://www.ergocanada.com/ergo/keyboards/mechanical_vs_membrane_keyswitches
..html>

I learned to type in high school on an Olympia manual. I typed at home on a
Smith-Corona electric. Both have excellent, though quite different,
keyboards.

In 1980, I was introduced to the pleasures of an IBM buckling-spring
keyboard. That was it. In the intervening 30+ years, nothing has ever come
remotely close. Tens of thousands of male typists will agree. It is in a
class by itself.
 
W

William Sommerwerck

I'll admit that I rather liked the way these keyboards
worked. However, I can go faster and type longer with
current generations of low-travel keyboards.

As Captain Redbeard Rum (Tom Baker) says in the "Potato" episode of "The
Black Adder" -- "You have a woman's hands!"
Real men don't use wimpy keyboards.

Absolutely. For most men, a short-stroke keyboad -- the IBM's Selectric
being the notorious example -- is anathema. (It took 20 years of random
exposure to the Selectric for me to gain some degree of comfort with it.)

The Smith-Corona electric portables had a similarly long stroke that
appealed to make typists. When Consumer Reports tested typewriters 50 years
ago (I'm old, I'm old!), the panel strongly preferred the Olympia manual and
the Smith-Corona electric portable -- my preferences, exactly.

For those out there wondering what this is all about... The preference for
the IBM Model M and its ilk among male typists is /almost/ universal. It is
"Das Klavier". I used to work with Charles Frankston (Bob's brother) who was
also an M freak. He had a drawer full of them, and would sometimes wave one
in my face: "Look what I have, and you don't!"
Yeah, there's nothing like 70 grams force and 6 mm travel
for the Model M, as opposed to about 20 grams and 2 mm
today's keyboard. Try a glass keyboard (iPad) with about
3 grams of force and zero travel.

<shivers>

A short, easy throw does not a good keyboard make. The Model M's long stroke
and non-linear relationship between force and displacement provide
mechanical feedback that makes it posible to type faster and with fewer
errors. Most users notice this immediately.

Drivel: I play piano and synthesizer. It's much the same
as computah keyboards. The piano/organ/synthesizer
keyboards all look similar, but it doesn't take much in the
way of tiny differences in key size and key action to foul
me up. It takes me a few minutes of fumbling to get used
to a new keyboard.

I don't play a musical instrument. But I once compared a Steinway with the
Baldwin SD-10. The keyboard action was completely different. This might have
been what ultimately drove Baldwin out of business.
 
W

William Sommerwerck

I appreciate the compliments, Arfa.

I'm an aggressive editor, and really "lay into" a piece if I think it needs
it. (Most do.) My experience has been that most editors are "wussy", and
don't begin to do what's needed to improve.

When Jacqueline Kennedy was alive, "Esquire" (a porno-free men's magazine
that predates "Playboy" by 20 years) poked merciless fun at Ms Bouvier's
stint as an editor at a major publisher. "Mr Pynchon, I found a period in
the wrong place on page 275, and there's a semicolon on page 681 that I'm
not sure of, but otherwise, I don't see anything wrong." (Thomas Pynchon
writes immense novels, such as "Gravity's Rainbow".)

http://en.wikipedia.org/wiki/Thomas_Pynchon

I do not, however, change anything for the sake of changing it. I can defend
every change I make, though the author might not always agree. My goals are
simplicity and clarity -- especially for readers not familiar with the
material at hand.

Most writers (myself included) overwrite, using too many words and
pointlessly repeating ideas (while omitting important material). One of the
effects of "paring down" the writing is that the piece becomes easier to
read and understand. I also change words for a more-exact or vivid ones. I
try to make the piece engaging, something that a reader will want to read,
and enjoy reading.

I was not generally happy with the editing my work received at "Stereophile"
and "The Audio Amateur". Ed Dell, publisher of the latter, apologized,
saying that he couldn't find really good people. Not surprisingly, the
magazine couldn't afford to hire good editors.

I'm a degreed EE, so I'm not working from a position of total ignorance. If
I don't know something, I check Wikipedia (which has lots of technical
articles, of widely varying usefulness) and the Web. I high whatever points
of confusion remain, so my boss can fix them (if he chooses).

One of /the/ great pieces of technical writing is Philbrick's book on op
amps. It's nearly 50 years old, but still has all sorts of useful
information, with the most-amazing indexing and cross-referencing you will
ever see in a book. Your jaw will drop. It's also a "good read". I cut my
op-amp teeth on it 40 years ago, and several years back an engineer in a
UseNet group (perhaps this one) sent me a copy. I treasure it.


Unfortunately, I think that the skill levels of many editors, don't match
those which you seem to possess. I think that many believe that just because
an article has been passed to them for 'editing', it must then be altered
and generally 'messed about' in order to justify the fact that it *has* been
passed to them, and that they have earned their fee. I have had articles
that I've written, totally mauled by an insensitive hand. Words and phrases
that I've chosen very carefully have been changed or removed, resulting in
(sometimes) a complete reversal of the intention of a whole paragraph, let
alone a sentence, indicating that the editor had no understanding of the
subject material, nor the people who were its targeted readers.
I have also had grammatically correct structures changed into ones that are
not, and correct spellings changed for wrong ones. By the same token, I
became very close to the editor of one magazine that I wrote for, and he
told me that my copy was a pleasure for him to work with, because the only
'editing' that he ever had to do to it, was an occasional slight precis-ing
of a paragraph to make the article fit the space available. This was always
done very carefully and sensitively so as to impact on the content as little
as possible.
 
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