I am not questioning the nasty embrittlement shown in your pictures, but  am
questioning what the heck you used to solder it with - what kind of solder.

Further I am questioning whether or not the device was operated after you
soldered it and before you decided to photograph it - is this a failure or
return.

One problem that I do note, is that you have failed to properly trim and
form the leads prior to mounting and soldering the device.

Typically RF transistors or amplifiers can get pretty hot, and if they are
board mounted, and their ground leads, where most or all of the heat is
going to escape, are cut too short, and not properly formed, and not
properly soldered, then gold or no gold, they are going to cause normal
tin-lead solder to reflow during operation.

It is vital, absolutely vital, that all ribbon leads of these types of
devices be completely flat on the circuit board trace before they are
soldered, gold or not, and it is obvious in these pictures that that is not
the case.

One final issue, and I am sticking my neck out here, since I do not know
exactly what the device is (part type and number), and I do not have any
data sheets, and I do not know the recommended mounting for this particular
device. Generally speaking, RF type transistors are mounted on a Heat Sink
under the PCB, with the body of the transistor going thru a hole in the PCB
and being mounted such that the leads lay flat on the corresponding PCB
traces. On smaller devices such as this, it is critical that lead forming is
done, and that that lead forming must account for thermal expansions over
the entire operational temperature range of the device, and if the ceramic
case has a metal bottom, and it is soldered to the board, then the lead
forming must account not only for the entire operational temperature range,
but for the soldering operation itself.

Finally, these devices must be hand soldered, and hand soldered by someone
who knows how to solder these types of devices.

Simply from observing the pictures, I would say that the ground leads are
way too short to transfer the heat that whoever required the large holes
knew was going to be there, and that the leads were not properly formed, and
that whoever soldered the leads did not know how to solder them, and spent
way too much time on the solder joint, thus the excessive embrittlement
(once again, I am not arguing the embrittlement issue itself, but this
appears to be excessive).

Please remember that tin-lead solder is an exceptionally poor electrical
conductor, and that it's conductivity is only 16% to 18% that of copper, and
that its thermal conductivity is equally as bad. This means that if you
install any ribbon lead device such as this, whether it is an RF transistor
or amplifier or not, that if the leads are just 'hanging out there', with
lots of solder between them and the trace on the board, which in terms of
both current and thermal flow is now a resistor, then the device will very
quickly get hot enough to reflow the solder on the leads.

Any and all of the above are probably contributors to why these pictures
look soooooooo ugly!

Yes, there is gold embrittlement, but I saying that this is not just gold
embrittlement, but that there is more to the issue of the joints shown in
these pictures.

Even when hand soldering a device such as this, and even if the leads are
properly formed, it is good practice, and common practice, to hold the lead
firmly against the trace during soldering with something such as the tip of
a dental pick, or some other similar object (even a wooden toothpick or the
wooden end of an alcohol swab) that will not interfere with the flow of
solder, or thermally interfere, but that can he held there completely still
until the solder joint has thoroughly cooled.

In other words, what I am saying, is that in this case, even if all the gold
were removed from the leads prior to soldering, you would still have
problems with them, which at best would be cold solder joints at
installation, and/or reflow during operation.

Forgive me, but these solder joints look like crap, to put it bluntly (and
mildly), irrespective of the gold embrittlement.

JaMi


----- Original Message -----
From: "Ingemar Hernefjord (KC/EMW)" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, November 06, 2006 12:59 AM
Subject: Re: [TN] Gold Embrittlement


Agree,
We degold all microwave SMT small outline transistors ("helicopters"),
because we had catastrophic gold embrittlement problems. The solder
joints were so brittle, that the leads lifted from the pad in the temp
cycle tests. We measured as much as 15 micrometers of gold! The
semiconductor manufacturer meant, that it is a problem to have control
on the gold process on such small parts. What nonsense! Anyway, we are
today suspiscious with many gold plated parts and do degolding rather
than getting embrittlement.

I'll send some pictures to Steve, so you can see what can happen.
Horror!


Inge


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: den 2 november 2006 23:06
To: [log in to unmask]
Subject: Re: [TN] Gold Embrittlement

Hi Amol,
I you have imersion Au, Au-embrittlement is not a problem because there
is not enough Au. Be careful, however, if your PCBs come from China; I
have seen much thicker Au-layers than are possible with iAu.
Calculating the wt% of Au in a soldert joint is an exercise in futility,
because you have to make the assumption--frequently not warranted--that
the SnAu-IMCs are uniformally distributed.
In cases where you suspect thicker Au [and for the matter Ag; which is
equally as bad as Au in causing SJ-embrittlement] deposits, the safest
course of action is to wash the Au (Ag) off by tipping.

Werner

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