The transistor in your photograph is a Freescale 9
Shawn,
The transistor in your photograph is a Freescale 900MHz 60W RF Power
MOSFET. The epoxy seal around the ceramic lid of the transistor appears
to be intact. Even if it wasn't there is nothing that is going to leak
out of the transistor package to cause the kind of growth seen in your
photograph. The growth appears to be limited to the drain (i.e.,
output) lead of the transistor. The bias of the drain lead is most
likely 26 to 30VDC and there would also, as Ingemar pointed out lots of
RF current in this area. Do you know what solder paste was used to
solder the power transistor? With the DC bias, high RF current and high
temperature one has the conditions to accelerate corrosion especially if
there are flux residues or other contaminates present. I'm assuming
that you removed the lid from the power amplifier when it stopped
working to take the photograph and it wasn't just sitting on your desk
exposed. If it was something corrosive might have dropped on the power
transistor.
Regards,
George
George M. Wenger
Andrew Wireless Solutions
Senior Principal FMA / Reliability Engineer
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 (office) (732) 309-8964 (cell)
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave Elder
Sent: Tuesday, June 24, 2008 3:55 PM
To: [log in to unmask]
Subject: Re: [TN] Power amplifier growth
Thanks for the thoughts, Shawn.
We are still investigating the source of the "growth".
No, the transistor no longer works.
Cheers, Dave
Upton, Shawn wrote, On 25/06/2008 1:14 a.m.:
> I wonder though if temp spiked suddenly, enough to cook the part but
> not enough to heat up the PCB? Well, above what the PCB had already
> been cooked--it does have some discoloration. I'm wondering about
> sudden spike, then the transistor goes open circuit. Fast enough to
> blow the guts out, but not long enough to discolor the pcb above and
> beyond what it has already seen.
>
> Thermal compound and/or flux residue interacting with whatever leaked
> out of the power transistor when it went? Almost looks like is left
> over in the oven when a pie (high in sugar) has a spillover.
>
> Lastly, just to verify: the transistor is bad, right? Or is it still
> working?
>
> Shawn Upton, KB1CKT
> Test Engineer
> Allegro MicroSystems, Inc
> [log in to unmask]
> 603.626.2429/fax: 603.641.5336
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
> Sent: Tuesday, June 24, 2008 5:04 AM
> To: [log in to unmask]
> Subject: Re: [TN] Power amplifier growth
>
> Looks like less of a growth and more of transmogrification.
> Looks like Q100 got pretty hot.
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave Elder
> Sent: Tuesday, June 24, 2008 1:01 AM
> To: [log in to unmask]
> Subject: [TN] Power amplifier growth
>
> Has anyone seen anything like this?
> The growth is on a 100W power amplifier that has been sitting, powered
> up, under load, on a desk, for six months.
>
> Dave
>
> http://sites.google.com/site/taitpcb/
>
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