Jerry,
I appreciate Mike's comments regarding peaks. We also strive for a lower peak
temperature than the 245. The 210 C nominal - with a peak of 230 C maximum is
what we work with. We utilize a no-clean paste, and incorporated the
manufacturer's recommendations for a more 'tent' like preheat section as well.
Solder joint quality has improved. The no-clean provides the added benefit of
longer stencil life as well.
The 90/10 compositions for lead materials have been what I have found in lead
frame analysis as well. This does change what actual alloy exists in the solder
joint during reflow (high melting point than Sn63/Pb37), but I want to maintain
component integrity, so keep to the less than 230 C peak.
Cordially,
Mary Smoot
Process Engineer
Lexmark Electronics
[log in to unmask]
[log in to unmask] on 11/12/98 05:38:48 PM
Please respond to [log in to unmask]; Please respond to
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To: [log in to unmask]
cc: (bcc: Mary Smoot/Lex/Lexmark)
Subject: Re: [TN] Assy: QFP leadframe tin-lead finish
Jerry,
We have also seen this issue with this plating composition. When
we contacted the IC manufacturer's process applications group, they also
stated the need for elevated reflow temperatures. They suggested a peak
temperature of up to 245C for 30 seconds (huh?). Being the kinda guy who
likes 215-220 max to protect my little babies, I took this with a large
grain of salt. And when I tried it, I still saw no real improvement
(except for parts jumping around going "yowza, that's hot!"). What
finally worked for us was an adjustment in the original profile in the
soak section. We are using an aqueous paste that has a typical
recommended ramp/soak/ramp/peak/cool profile. What we discovered was
that the extended soak was diminishing/killing off the activators in the
paste causing poor wetting. We adjusted it to a more 'tent shaped'
profile to cut back the extended soak period and a shortened time base
overall, and saw vast improvements in the wetting of both QFPs and
TSOPs. This may work for you also, as no-cleans have an even
lower/milder level of activators. Good luck....
Mike McMonagle
PCA Process Engineering Supervisor
K*Tec Electronics
1111 Gillingham Lane
Sugar Land, TX 77478
(281) 243-5639 Phone
(281) 243-5539 Fax
[log in to unmask]
> -----Original Message-----
> From: Jerry Cupples [SMTP:[log in to unmask]]
> Sent: Wednesday, November 11, 1998 5:37 PM
> To: [log in to unmask]
> Subject: [TN] Assy: QFP leadframe tin-lead finish
>
> Hello, TechNet:
>
> Reviewing an IC component specification here, we find the plated
> finish of
> 300-800 microinches 85/15 Sn-Pb. Many other spec sheets simply call
> for an
> Sn-Pb finish. The part in question seems to wet poorly, forming very
> shallow fillets.
>
> Can anyone confirm the typical fusible tin-lead alloy for QFP
> leadframes is
> more like eutectic composition?
>
>
> thanks,
>
>
>
> Jerry Cupples
> Interphase Corporation
> Dallas, TX USA
> http://www.iphase.com
>
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