Hi TechNet! Just to echo/add to George's Pd comments - we have found that
the Pd finish is very flux dependent and you can either recalibrate your
inspectors or change fluxes. We have found that using the correct flux will
result in a solder joint that doesn't have the "alligator" or "foot in the
mud" appearance. We have also found that an inert environment (N2 in reflow
or the Vapor Phase chemistries) will help greatly in achieving "typical"
solder joint wetting angles. And as George mentioned, Pd is a "getter"
element - it is used in mufflers, it is used to seed plated thru holes for
plating operations, etc. TI has begun putting a flash of Immersion gold on
their Pd/Ni lead finish for the purpose of closing off the Pd surface to
the environment. The flash of immersion gold has resulted in a considerable
improvement on the wettability of their component leads and made the Pd/Ni
finish much less flux sensitive. A Immersion gold/Pd/Ni surface finish is
also a very wirebondable surface finish in Chip On Board applications.
Dave Hillman
Rockwell Collins
[log in to unmask]
"Wenger, George M." <[log in to unmask]>@ipc.org> on 05/09/2002 12:11:48
PM
Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
to "Wenger, George M." <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
To: [log in to unmask]
cc:
Subject: Re: [TN] Palladium Leads
The one thing you need to keep in mind is that Pd does what it does in a
muffler (i.e., pulls things out of the environment) so you need to know
your "environment" and the "environment" the parts were exposed to before
you received them in order to know anything about their solderability and
shelf life.
In my previous company we used lots of TI PdNi plated IC packages. Our
assembly engineers would rather have used SnPb plated packages but most
times you may not have a choice. Most assembly engineers usually don't
have many choices. Even if they get components that have horrible
solderability the answer usually is we need to build product so use them
and will scream at the component vendor later. Most of the reliability
studies I've seen or conducted have shown solder joints made to PdNi plated
components meet most solder joint integrity/reliability requirements. The
reason assembly engineers don't like PdNi plated components is because the
solder joints look different than those made to SnPb plated components.
Assembly engineers in my previous company typically used a single profile
for forced convection reflow surface mounting of a given product. They
usually didn't increase the temperature because there were some PdNi plated
components on their boards. We used to refer to solder joints made to PdNi
plated parts as having an "alligator" surface texture rather than a smooth
shiny surface. Metallurgical evaluations indicated that the surface
texture us due to concentrations of pd near the surface. If we increased
reflow profiles 5 to 10C hotter the "alligator" texture would be less
pronounced. What we wound up doing was retraining operators and providing
visual aids for inspectors.
We did have at least one case where we had PdNi plated parts that won't
solder. The component vendor indicated that there was organic
contamination of the components before we received them.
Regards,
George
George M. Wenger (908)-546-4531 [log in to unmask]
Distinguished Member Technical Staff
Celiant Corporation, FMA Lab, 40 Technology Drive, NJ 07059
-----Original Message-----
From: Guy Ramsey [mailto:[log in to unmask]]
Sent: Thursday, May 09, 2002 11:20 AM
To: [log in to unmask]
Subject: Re: [TN] Palladium Leads
I did a little search on the web and found that TI claims eight years when
stored in their packaging . . . three years outside of it . . . HA!
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Earl Moon
> Sent: Thursday, May 09, 2002 9:07 AM
> To: [log in to unmask]
> Subject: Re: [TN] Palladium Leads
>
>
> Bev and others,
>
> I've worked with Pd in one way or another, starting with hybrids in the
> '60's but never thought about solderability over time. What is the
"shelf"
> life of Pd compared, say, with SnPb? Know the question is too general but
> any guesses?
>
> Earl
> ----- Original Message -----
> From: "Bev Christian" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, May 09, 2002 7:59 AM
> Subject: Re: [TN] Palladium Leads
>
>
> > Henry,
> > Back in the mid 90's when these parts (TI palladium plated) were
> introduced
> > in the company I worked at then, we had some teething problems.
> But with
> > some profile manipulation and training of operators we did not have any
> > issues (Of course there was lab testing in the background).
> The training
> > had to be done because there will be more wetting angles closer to 90
> > degrees than they are used to.
> >
> > One other very important thing, this finish and I suppose other
> palladium
> > finishes, is/are finicky when it comes to fluxes. Some no-cleans work,
> > others don't. We were lucky our old standard fluxes - Kester
> R243 solder
> > paste and 923 and 924FB wave solder fluxes worked well. Others didn't.
> >
> > And finally, how old are your parts and what conditions have they been
> > stored in? I'm sure others will come up with other good questions and
> > hopefully a few hints for you.
> >
> > regards,
> > Bev Christian
> > Research in Motion
> >
> > -----Original Message-----
> > From: Henry Rekers [mailto:[log in to unmask]]
> > Sent: May 8, 2002 8:33 PM
> > To: [log in to unmask]
> > Subject: [TN] Palladium Leads
> >
> >
> > Has anybody out there experienced non-wetting problems with no-clean
> > solderpastes on parts that have palladium coatings on the leads.
> > Specifically, have you had this problem with Texas Instruments parts?
> >
> > Thanks.
> >
> > Henry J. Rekers
> > Manufacturing Engineer
> >
> >
>
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