Sal ammoniac is still commonly used as a tip tinning compound today. Many things change, but some good things stay the same.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ed Popielarski
Sent: Wednesday, March 02, 2011 11:53 AM
To: [log in to unmask]
Subject: Re: [TN] Interesting little story. Sounds vaguely familiar for me at least
Inge,
You might be remembering this:
http://en.wikipedia.org/wiki/Sal_ammoniac
Regards,
Ed Popielarski
Sr. Mfg. Engr.
NBS Corporation
2950 Patrick Henry Dr.
Santa Clara, Ca. 95054
Ph: 408-654-1100
Fx: 408-654-1107
Cl: 408-234-1497
Cl: 949-581-6601
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord
Sent: Wednesday, March 02, 2011 2:56 AM
To: [log in to unmask]
Subject: Re: [TN] Interesting little story. Sounds vaguely familiar for
me at least
Very familiar indeed.
I remember, when I was a little kid, my grandfather was doing some
repair of
his old Philips radio. He heated his old fashioned soldering iron in the
wood stove, then gave it one or two strokes against a piece of salmiak
(?)
and dipped the component's terminal in a thick flux paste and finished
the
operation by soldering. It hissed and lots of stinky smoke filled the
room.
That was probably the start of my interest for electronics. The golden
painted electron tubes fascinated me, also how the magic eye fluctuated
when
he was tuning in London BBC.
Inge
On 1 March 2011 20:19, Gene Felder <[log in to unmask]> wrote:
> If you guys had not seen this article, I thought you would enjoy it.
>
> See
>
>
http://www.jameco.com/jameco/workshop/techtip/smt.html?CID=March11NL3355
763&
> sp_rid=MTgyNDYwMTE3NzkS1&sp_mid=3355763
>
> SMT Soldering Nightmare
> Submitted by an anonymous Jameco Customer
>
> Hi Everyone,
>
> "I just thought I should share my SMT soldering experience. A
particular
> chip I wanted to use, specifically a USB-enabled microcontroller, came
only
> in an SMT package (44 pins at 0.8mm spacing). I wasn't confident, but
I
> figured I could do this. My iron was old and clumsy, but with careful
> application of delicate quantities of solder, lots of flux, and a reel
of
> wick I thought I could make do. I've done some passive component work
in
> the
> past and they came out fine.
>
> The soldering went okay. Messy, with all the flux and solder bridges
> between
> pins, but with a little more heat, the wick sucked the excess away.
Careful
> metering showed all the connections were good. I realized that I
needed
> sharp meter probes for this. The blunt ones are safer, but I needed a
sharp
> one to be sure I'm on the pad at one end and on the pin at the other.
While
> I won't try this at home, I've seen a professional use scalpel blades
> welded
> to his meter probes just to get them sharp enough.
>
> Testing was the key, and I tested for both shorts between pins (most
> common)
> and open connections (they happen too). To fix a bridge, a quick dab
of
> some
> more flux, and a bit of wick was an easy fix. I heated it up and
watched
> the
> excess solder slurp away. I was careful not to over do it because it's
easy
> enough to get an open connection instead. With every repair came new
> testing
> to make sure I wasn't going backward.
>
> Fighting back the nerves after testing, fixing and retesting, I
plugged it
> in and turned it on! Smoke came out of the chip. Not good, but I guess
it
> makes for a more interesting story.
>
> This required more inspection of the board layout and more testing. I
found
> a few minor concerns that were easy enough to fix. Sadly, however, my
> patient died on the table. The chip was no longer working and was
> pronounced
> dead due to a hard short across the power rails.
>
> To remove the corpse I used a hot air gun, usually used for shrinking
> heat-shrink tubing. It runs much hotter than your typical hair-dryer,
so
> don't use it for that, but for heating things, it works quite well. I
> clamped up the board and began directing heat over the chip. Sadly, my
> strategy was a bit south of perfection, for my plastic parts (sockets,
etc)
> began to melt.
>
> I stopped and regrouped, electing to make myself a heat shield out of
> aluminum foil. The foil wraps around the board and covers all the
> components, except where I've razored out a little square to clear the
> now-dead chip. This worked although the nearby plastic parts still
melt a
> little, but they were still functional and now had a bit of extra
> personality.
>
> While blowing heat, I lightly pick at the chip with a long sharp awl,
and
> eventually (this took some time) it popped loose and fell off the
board,
> off
> of the table and onto my lap. I was wearing shorts. It was hot and it
hurt!
> Fortunately, the chip wasn't very large and only left a small souvenir
of
> the experience.
>
> The circuit board clamp, however, offered more resistance, and I
managed to
> singe a couple of fingertips along the way. Now I cleaned off the pads
with
> more flux and wick, I addressed the board layout concerns, and it was
time
> to stick down a fresh new chip. It went well with a similar procedure.
All
> the connections, including the edited ones on the PCB layout, tested
out
> fine. I cross-checked it with the specification sheet to confirm I had
done
> it correctly.
>
> I pulled out my handy little microscope and also did a visual
inspection
> this time of the solder joints. I was ready to try again. Power
connected.
> Checked for polarity. All was well, until I turned it on.
>
> Fizzle. Smoke. Pop.
>
> Another board was inspected, edited, and provided, in case something
was
> wrong with the first one. Another chip was installed, with an absolute
> minimum of supporting components.
>
> Fizzle. Smoke. Pop.
>
> Fortunately I had purchased quite a few of these chips. Much more
checking
> ensued. On-line designs for similar boards were cross-checked with the
chip
> spec sheet. The spec sheet was crossed with the schematic. The entire
> schematic was carefully metered out with a continuity checker,
including
> possible shorts. All appeared well.
>
> But the chips kept going up in smoke. A few more iterations of
aluminum
> foil
> and heat-gun work, plus several more hours sticking down and testing
more
> chips, resulted only in more burnt chips.
>
> At this point you must be wondering if this story is going to have a
happy
> ending. Time passed as did the waves of frustration before I was
finally
> able to establish what may have been the problem. It wasn't a
soldering
> problem, a circuit board layout issue, personal ESD discharge, the
solder
> or
> the flux I used. Then I started to think that maybe it was the
soldering
> iron itself that was the problem.
>
> Never missing an opportunity to buy some new gear from my friends at
> Jameco,
> I bought a new iron with a properly grounded tip and a much finer tip
at
> that. I stuck down yet another chip, and it worked without drawing
> excessive
> current and/or boiling itself. Yes... It seems at the moment it was my
> soldering iron that was destroying these things. Further experiments
are
> still in progress.
>
> A brief note to all my fellow hobbyists who might want to try SMT
work. You
> should get an ESD-specified soldering iron for anything more
complicated
> than surface-mount passive components!"
>
> Gene Felder
> [log in to unmask]
>
>
>
>
>
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