Wayne,
Thanks for the data,but your final statement puzzles me.You stated that
since the temperatures were going higher and the cycle times were longer the
data didn't warrant any concerns.It appears to me it would warrant some long
term reliability concerns.Did I miss something?
Dewey
> -----Original Message-----
> From: R. Wayne Johnson [SMTP:[log in to unmask]]
> Sent: Thursday, August 09, 2001 9:07 AM
> To: [log in to unmask]
> Subject: Re: [LF] Antw: Re: [LF] Eutectic alloys?????
>
> Hi all,
>
> The published reliability data on lead free alloys is limited. However,
> the NCMS report from 1997 showed that with 1206 chip resistors, the alloys
> Sn96Ag2.6Cu0.8Sb0.5 and Sn77.2In20Ag2.8 did not perform as well as
> eutectic SnPb in the 0 to +100C, 30 min Cycle, 5 min Dwell thermal cycle
> test and that Sn96.5Ag3.5, Sn95Ag3Bi2, Sn96Ag2.6Cu0.8Sb0.5,
> Sn77.2In20Ag2.8 and Sn95Ag3.5Zn1Cu.5 all did not perform as well as
> eutectic SnPb in the -55 to +125C, 72 min Cycle, 20 min Dwell thermal
> cycle test. The NCMS study did not specifically look at the SnAgCu
> eutectic, but at SnAg and SnAgCu eutectic with a fourth element additive.
>
>
> In more recent work, IBM presented a paper "Thermomechanical Fatigue
> Behavior of Selected Lead-Free Solders" at APEX 2001 that showed with a
> ceramic BGA, the thermal cycle reliability was better with
> Sn-3.5%Ag-3.0%Bi (SAB) and Sn-3.8%-Ag-0.7%Cu (SAC) than the eutectic SnPb
> over the temperature range from 0C to +100C, but the advantage decreased
> as the time (30min vs 240min) of the cycle increased. Furthermore, when
> the cycle temperature range increased to -40C to +125C the
> Sn-3.8%-Ag-0.7%Cu (SAC) alloy performed worse than the SnPb eutectic.
> This data indicates that increasing the length of the cycle or increasing
> the temperature range decreases the reliability of the SnAgCu alloy more
> than the SnPb alloy.
>
> We have 1206 chip resistors and PBGAs in thermal cycle from -40C to +150C,
> 90 minute cycle with 20 minute soaks. The results to date show a
> significantly lower thermal cycle life (~50%) with the 1206 chip resistors
> and the SnAgCu alloy compared to the SnPb. We have insufficient BGA
> failures to estimate reliability at this point, but the first failure was
> with the SnAgCu alloy (solder ball and paste). The test is ongoing.
>
> Since underhood automotive temperatures are at 125C and going higher and
> the cycles are typically long, the currently available data does warrant
> concern over the use of SnAgCu for underhood automotive applications. We
> are working to develop additional reliability data and understand the
> failure mechanisms.
>
> Wayne
> Center for Advanced Vehicle Electronics
> Auburn University
>
>
>
>
>
>
> At 01:44 PM 8/9/01 +0200, Guenter Grossmann wrote:
> >Lee
> >
> >I haven't any data so far to support any claim that lead free solder
> alloys are more or less reliable than Tin-Lead alloys. However, looking at
> data published so far that I am aware of I would like to make the
> following comments:
> >- Most of the lead free alloys creep slower than tin-lead
> >- It is not correct to conclude that because of this fact the lead free
> alloys are more reliable that tin-lead .
> >- Temperature cycling tests run so far are highly accelerated (steep
> ramps, short dwell time). The fact that in these tests the lead free
> alloys show a better performance does in my opinion not say that they have
> a better resistance than tin-lead. Primarily they show that tin- lead sees
> more strain during each cycle of the test.
> >
> >I hope I can provide some comparative data by the end of this year. We
> made some PCB's with LCCC's ( 24 connectors pure tin) on FR4 with some
> lead free alloys ( SnAgCu, Castin, SnZn, SnAg, SnPbAg ) and right now they
> are in a slow thermal cycling test ( -20°C, 120°C; ramp 2- 4°C/min, dwell
> time 30 min at -20°C, 10 min at 120°C).
> >
> >Best regards
> >
> >Guenter
> >
> >Guenter Grossmann
> >
> >Swiss Federal Institute for Materials Testing and Research EMPA
> >Centre for Reliability
> >8600 Duebendorf
> >Switzerland
> >
> >Phone: xx41 1 823 4279
> >Fax : xx41 1823 4054
> >mail: [log in to unmask]
> >
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> >
> R. Wayne Johnson
> Alumni Professor
> Electrical & Computer Engineering
> Auburn University
> 162 Broun Hall
> Auburn, AL 36849-5201
> 334-844-1880 (tel)
> 334-844-1898 (fax)
> [log in to unmask]
> http://www.eng.auburn.edu/department/ee/leap/
> http://www.eng.auburn.edu/department/ee/cave/
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