Dear E-mail forum mailers;
I do agree on opinion of Dr. Hermann of Fraunhofer IZM.
I'd also tested UBM reliability of Ni/Pd for Pb-free solders(Sn-Ag-Cu, Sn-Ag) for lead frame CSP.
I carried out board level reliability and ball shear test.
After board level solder joint test, It showed very lower solder joint reliability than other UBM, such as Ni/Sn. Crack was found to propagate along the interface.
I represented this result at TMS 2000 meeting held in Nashville, US.
This paper will be published in JEM (Journal of Electronic Materials), end of this year.
In comparison of other Pb-free solder electroplating system such as pure Sn, Sn-Bi, Sn-Cu etc,
N/Pd has lower wetting properties in leaded Packages such as SOJ, TSOP etc. (You may know it well.)
And Ni/Pd's adhesion with EMC is very weak, So, If we apply Ni/Pd plated leadframe to high temperature SMT process, package reliability itself is very questionable.
In case of conventional type package such as QFP or TSOP-I, they had lower pakcage-level reliability after Tmax=260C reflow pretest condition.
Other problem is microcrack occurred during form process, that is, making a lead shape. Someone said that it could be fixed with optimization of plating condition and form process parameters. But it always have some possiblites of crack and other defects(including Au wire boniding problems).
Well, Ni/Pd will be an alternative to lower-reliability required application.
But it is not reasonable to apply it to normal package case, especially to Pb-free solution.
Thanks for reading and any questions.
Sincerely Yours,
**********************************************
Seung Wook Yoon
Ph.D, Research Staff
Module/Package Team
Semiconductor Research Division
Hyundai Electronics Industries Co., Ltd.
San 136-1, Ami-ri, Bubal-eub, Ichon-si,
Kyoungki-do, 467-701 Korea
Tel 82-336-630-4564
Fax 82-336-630-2338
http://exodus.kaist.ac.kr/~ytriumph
**********************************************
----- Original Message -----
From: "Dr. Hermann Oppermann" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, June 28, 2000 8:16 PM
Subject: Re: [LF] Texas Instruments Lead-Free Solutions - right solution?
> Is Palladium really an acceptable choice for solder joints?
>
> We have worked with Palladium as an underbump metallization for silicon
> chips. After bump formation with SnPb solder we investigated the
> reactions of the solder with Palladium in reliability tests. We observed
> a very fast growth of various Pd-Sn intermetallics which were consuming
> most of the tin in the solder. In addition the intermetallic phases
> PdSn3 and PdSn4 growed perpendicular to the layer formed as large plates
> into the solder. The measured growth rate of intermetallics was so large
> that even the bump shape changes with time from ball to prolonged posts.
> After a few hundred hours at 125°C no tin could be found in the solder
> anymore. Pure lead remains between the intermetallic plates and on top
> of the solder bump. Shear values decreased dramaticly by high
> temperature storage. The same was found after longer time storage at
> 85°C as well. All this we published at 3rd 1999 IEMT/IMC Symposium on
> „Microelectronics Packaging Innovation for the New Century? April
> 21-23, 1999, Sonic-City ?Omiya, Tokyo, Japan.
>
> Because nearly all solders contain large quantities of tin we expect
> these reactions of tin and Palladium in lead-free solders as well. Did
> anyone investigate this already and could share these results?
>
> Regards,
>
> Hermann
>
> --
> Dr. Hermann Oppermann
> Fraunhofer IZM
> Gustav-Meyer-Allee 25
> D-13355 Berlin, Germany
> --------------------------------------------------
> phone: +49-30-46403-163, -160
> Fax: +49-30-46403-161
> email: [log in to unmask]
> --------------------------------------------------
> Dept. Chip Interconnection Technologies
> Group Optoelectronics, HF and Sensor Integration
> http://www.izm.fhg.de/
> http://www.izm.fhg.de/avt/index.htm
> http://www.izm.fhg.de/avt/opperm.htm
> --------------------------------------------------
>
> "Romm, Doug" schrieb:
>
> > For anyone interested, you can view the TI Lead-Free
> > Solutions Web Page at the following link:
> >
> > http://www.ti.com/sc/leadfree
> >
> > Of couse the contents of this page will be updated as new
> > information becomes available.
> > Regards,
> > Doug Romm
> >
>
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