Hi IPC-LeadFree Listserve
 and TI-DougR,

Now that I am a bit more familiar with how the IPC forum shows messages
on the ipc.org site and rolls out one month and then in the next, I
want to come back to this July note exchange and ask some questions or
pose criticisms of the reports listed on the TI web site that Doug gave
us as www links. I have spent quite a bit of time digesting/reviewing
each reports. Thanks to Doug!! and Werner.

Being new to this forum hopefully this is the right way to have this
discussion. (Advice welcome if another way is better, yet provides
for some community involvement, and more knowledge)

For those who can't follow along please link and print out Doug's report.

On Tue, 8 Jul 2003 11:37:18 -0500, Romm, Doug <[log in to unmask]>
>Werner,
>
>Thanks very much for the feedback!  It's encouraging to get feedback
> from someone who has read our app notes on the web.
>
>I presume that you are referring to TI app note SZZA026 which is entitled>
<
< == I truncated Doug's intro == >
<
>This statement is made in app note SZZA 026 in reference to data generated
>in 2 separate app notes:
>
>1. Pb-Free Solder Joint Evaluation by Douglas W. Romm and Donald C. Abbott:
>http://www.ti.com/sc/docs/products/leadfree/pbfree_solder_eval.htm
>
>Under the section "Temperature Cycle Testing" on page 9 data us shown
>where of SnPb, NiPd, and NiPdAu finish components were soldered to PWBs
>using SnPb
>RMA, SnPb WS, and Castin Pb-free solder alloys.  For this experiment 10
>board-mounted units from each group were exposed to a temp cycle range of
>-65 deg C to +150 deg C for 3000 cycles. The units were removed from the
>temp cycle chamber at various read points and tested electrically.  The
>results in table 5 show that all of the lead finish and solder paste
>combinations passed electrical test out to 3000 cycles.
-----------------------------------

>http://www.ti.com/sc/docs/products/leadfree/pbfree_solder_eval.htm

Question/Comment:1 (page 1 the abstract's last paragraph)
 a)It is true that for lead pull the data was equivalent or better
 b)It isn't true for Thermal Cycling
  since as WernerE pointed out we really had no comparative data
  to choose one way or the other. I guess we could say equivalent
  yet this can be easily misunderstood.
 c)Visual is minimized
  For most of us, line operators, inspectors, and such, visual is
  a BIG item. In your write up you seemed to minimize it where in
  practice it becomes quite a hurtle.
  -That may have not been your intention yet on first reading
   this is how I interpreted "is visual only"
  -In a few recent presentations I have heard that due to visual
   many Lead Free joints would currently be rejected by the
   final quality inspectors.

Question/Comment:2 (page 4 Table 2)
 a)Here we see that for Contact Angle a Visual affect
   SnPb was visually superior. It wetted to a feather edge
   so an inspector would be very visually pleased.

Question/Comment:3 (page 4 Table 2)
 a)Run 9 showed a 32.8 angle for Ni-Pd-Au with Castin
   Did you have any thoughts on why this is so out of line
   considering your Wetting Balance results.

Question/Comment:4 (page 7 Figure 7)
 a)You have studied SnPb lead finishes soldered with Castin
   and I was wondering if you would agree to this combination.
   I understand from some other presentations that SnPb
   within a Lead Free solder structure has grain boundary
   problems and other.  Comments??

Question/Comment:5 (page 8 Temperature Cycling)
 a)You list -65 to 150 C for 3000 cycles
   Is this 30 minutes up and then 30 minutes down
   so that the test takes 3000 hours to complete?

Question/Comment:6 (page 8 Table 5
 a)When you took them out of the oven what was your pass
   fail electrical test. What it a DC Resistance Change?
   or was it an Open? I think Werner would prefer in-situ
   continual monitoring.
 b)From other testing with SnPb it is hard for me to believe
   that DC Resistance wouldn't change.

Question/Comment:7 (page 9 end of Table 6)
 a)Why did you stop cross sectioning at 250 cycles
   I have seen others, granted with chip capacitors, first
   start to see cracks at 300 cycles. It would have been
   interesting to see cross sections out through 3000

Question/Comment:8 (page 9 just below figure 8)
 a)Why did you switch to 60/40 rather than 63/37
 b)I wondered why you didn't do this Wetting Balance Test
   also with Castin particularly with Lead Free lead finishes
   since this would be the appropriate LF combination.

Question/Comment:9 (Table 7)
 a)Any thoughts or knowledge as to why the Wetting Balance
   Test disagrees with the Contact Angle measurements you
   showed earlier.

Again Thanks Doug, and Awaiting your relook at an old report.


YiEngr, MA/NY DDave

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