Hello DDave, collegues, & IPC LF Listservers


I will answer your questions regarding board and process you sent earlier
on the Shelf life evaluation we did.

The printed circuit board finish was NiAu finish and had been ordered
around 2.5 years before the test actually had been performed. Storage
condition: Office area with 20-25C and 30-60% humidity (not raining
inside...).
We used the testboard, since it was available from previous studies, no
special threatment, no bake, just out of the shelf and into solder paste
printing, placing, reflow. The board manufacturer is a small local german
one, low series volume support. we do not use production volume board
services for our test boards.

Other evaluations on OSP boards showed similar soldering performance,
except the pad edges sometimes.

The solderpaste, SnAgCu was chosen because SAC pastes are widely used at
European customers, and available from paste suppliers. Other alloys, for
example Sn3.5%Ag0.7%Cu showed similar results, no big difference. Most
difference on pastes is related to the flux chemistry. This paste was No
Clean paste.

The Reflow oven is the same we use for preconditioning our devices (Jedel
MSL) prior to reliability testing, therefore we use Nitrogen (around
1000ppm O2 or higher). We did earlier runs on NiPdAu devices with air
atmosphere, no visible difference if a good paste is used from our
experience. The mentioned study was done in Nitrogen atmosphere for machine
setup reason, not for the purpose getting 'better results'.

A rougher surface on SAC solders compared to SnPb solders is typical what
we see, common industry understanding too.

if questions, let us know

regards
Bernhard


At 10:25 30.07.2004, MA/NY DDave wrote:
>Hi Again TI-DougR, TI-DonA, Jowan, & IPC LF Listservers,
>
>Some more questions on the report by TI's technical threesome.
>
>In the soldering tests what was the Printed Circuit Board LF finish??
>- Ref: Page:12
>- I can kind of understand why you didn't list the paste manufacturer and
>may not list the PCB manufacturer yet it would be good to know the finish.
>
>Were the PCB's aged or were they all in excellent new condition??
>- Were they pretreated in anyway??
>
>Any particular reason you chose Sn4.0Ag0.5Cu as the LF alloy??
>
>Did you use Nitrogen reflow??
>- Ref: To me, yet maybe not to others, Many photos had soldering that
>looked rougher than SnPb yet (still) almost TOO good when I looked at the
>fillet.
>
>AGAIN, even if you chose not to reply on list or privately thanks for the
>report.
>
>Yours in Engineering, Dave
>Y i Engr, MA/NY DDave
>
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