LEADFREE Archives

July 2004

Leadfree@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
"Gupta, Munish" <[log in to unmask]>
Reply To:
(Leadfree Electronics Assembly Forum)
Date:
Wed, 14 Jul 2004 17:48:54 +0530
Content-Type:
text/plain
Parts/Attachments:
text/plain (173 lines)
Dear  Mr. Marc

Thanks  for  taking  time  to  educate  us.

Should  we  take  it  that  Alloy 42  lead  frames ( devices  in  SOT23
package etc)  are  exempted  from  post  bake  when  the  leads  are  100%
MATTE TIN  plated ! ! !


I  think  we  MISSED  the  hermetically  Sealed  METAL  CAN  packages.


One  really  gets  closer  to  the  subject  in  an  open  house
discussion.


regards
munish



----- Original Message -----
From: <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, July 14, 2004 5:29 PM
Subject: [LF] AW: [LF] Whisker test


> Dear all,
> Some comments on Annealing (developed, introduced and promoted by E4,
which is Infineon Technologies, Philips Semiconductors, STMicroelectronics,
Freescale Semiconductors)
>
> 1. Annealing is not a test, but a mitigation strategy to prevent whisker
formation
> 2. We prefer the word "bake", since annealing is an effect of second
order. Yes, recristallisation, dislocation slide and climb, recombination
and all these effects take place at 150 °C and result in a stress relieve
(if there is any stress prior to the baking), but the major effect is the
artificial growth of the intermetallic double layer Cu3Sn / Cu6Sn5 at the
Cu -Sn interface. This intermetallic layer grows regularly at 150 °C and
forms a continuous layer, which acts as a diffusion barrier for further
Cu-diffusion into tin. This Cu- diffusion is associated with the
intermetallic formation and happens only in the tin grain boundaries at RT
(--> irregulargroth of intermetallics), but due to a shift from grain
boundary diffusion in favour of bulk diffusion at higher temperatures at 150
°C, the layer is formed regularly. Since the intermetllic formation is
associated with a volume increase, the irregularities induce stress and have
to be avoided. This can be done by the introduction of addtional diffusion
barrier matals (Ni, Ag, ...) or by the artificaial growth of the
intermetallic itself.
>
> Thus bake can only be applied to Cu-based leadframes without additional
underlayer such as Ni or Ag or something else. It is also not applicable to
FeNi42 L/F since the mechanism for whisker formation is different (stress
induction during thermal cycling due to large cte mismatch of FeNi42 and Sn)
and also the intermetallics are different also the growth rate differs
significantly.
>
> Infineon does not make any difference in accordance to the pitch, but
applies 150 °C / 1h post plate bake to all components with Cu L/F and matt
pure tin plating.
>
> please find some of our publications on this issue for download at our
website
>
>
http://www.infineon.com/cgi/ecrm.dll/jsp/showfrontend.do?lang=EN&channel_oid
=-11663
>
> More publications and info available on request.
>
> regards,
> Marc Dittes, Infineon Technologies
>
>
> -----Ursprüngliche Nachricht-----
> Von: Leadfree [mailto:[log in to unmask]] Im Auftrag von Victor G. Hernandez
> Gesendet: Mittwoch, 14. Juli 2004 13:03
> An: [log in to unmask]
> Betreff: Re: [LF] Whisker test
>
>
> Fellow TechNetter:
>
>    Can someone share their understanding of the annealing process of
metals.
>
> Victor,
>
> -----Original Message-----
> From: Leadfree [mailto:[log in to unmask]] On Behalf Of Gupta, Munish
> Sent: Wednesday, July 14, 2004 3:46 AM
> To: [log in to unmask]
> Subject: [LF] Whisker test
>
>
> 14  july  04
>
>
> Need  expert inputs  only...
>
>
> Is  whisker  mitigation  strategy*  applicable  for  all  packages.
>
>
> A  big  package  like  TO220  where  leads  are  seperated  by  a  large
distance (much  greater  than  what  a  typical  length  of  whisker  is
> :
> 50um)  should  NOT  undergo  special  tests  like  annealing.
>
> Annealing  is  time  as  well  as  energy  consuming.
>
>
>
> *: bake  for  150C  @  1hr
>
> advised  by  ST , Philips , Infenion
>
>
>
> Any  comments  TONY ! ! !
>
>
> regards
> munish
> INDIA
>
> ------------------------------------------------------------------------
> -------Leadfee Mail List provided as a service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Leadfree To temporarily stop
delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL Search
previous postings at: http://listserv.ipc.org/archives Please visit IPC web
site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
> ------------------------------------------------------------------------
> -------
>
> --------------------------------------------------------------------------
-----Leadfee Mail List provided as a service by IPC using LISTSERV 1.8d To
unsubscribe, send a message to [log in to unmask] with following text in the
BODY (NOT the subject field): SIGNOFF Leadfree To temporarily stop delivery
of Leadree for vacation breaks send: SET Leadfree NOMAIL Search previous
postings at: http://listserv.ipc.org/archives Please visit IPC web site
http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information,
or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
> --------------------------------------------------------------------------
-----
>
> --------------------------------------------------------------------------
-----Leadfee Mail List provided as a service by IPC using LISTSERV 1.8d
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Leadfree
> To temporarily stop delivery of Leadree for vacation breaks send: SET
Leadfree NOMAIL
> Search previous postings at: http://listserv.ipc.org/archives
> Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
for additional information, or contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
> --------------------------------------------------------------------------
-----
>

-------------------------------------------------------------------------------Leadfee Mail List provided as a service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Leadfree
To temporarily stop delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL
Search previous postings at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-------------------------------------------------------------------------------

ATOM RSS1 RSS2