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TechNet E-Mail Forum <[log in to unmask]>, Hfjord <[log in to unmask]>
Date:
Tue, 7 Nov 2006 23:39:02 +0100
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Well Mr Besserwisser, you got no coffee today?

What you see is the situation BEFORE the whole solder process had to be
changed.
The poor ladies, who have been hand soldering helicopters for years, shouted
on me and
wondered why the joint could not be normal. Quick examination revealed that
the supplier
had put on gold that would suit better for a jeweler! We had to deliver, so
there was nothing
else to do than to degold all thousands transistors in a solder pot, by
means of a simple little
robotic.

The terminations are what the supplier sells on REELS for automatic
mounting, and we had no
time to wait for our purchaser to search the market for a emergency
shipping. So, we just had
to pick them all out of the reels and degold and handsolder them as usual.
There will be a juridic
case, be so sure.

These are low level signal amplifiers, no heat dissipated, cooling no
problem. We use heatsinked
transistors in other products, where heat is created. Don't you think we
know what to do and
how to design. We have mounted about 100,000,000 such transistors, dear MR!

The rest of your eructational pyrosis won't be met. I just showed an
interesting case of what
extremly thick gold on leads can cause, see it as a curiosum aurorum.

If the pictures are ugly, that may mirror the spectator's sight of the
world.

Best regards

Inge


----- Original Message -----
From: "JaMi Smith" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, November 07, 2006 9:27 PM
Subject: Re: [TN] Gold Embrittlement


>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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