TECHNET Archives

March 1997

TechNet@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:
[log in to unmask] (Jerry Cupples)
Date:
Tue, 25 Mar 1997 09:28:06 -0600
Content-Type:
text/plain
Parts/Attachments:
text/plain (54 lines)
Poh Kong Hui said:

>Hello Olly and Technetters,
>
>Could you tell me what is LQFP ?. And I am not too sure the meaning of
>"thicker version" of the std QFP....

No. Someone is always making up obscure acronyms, though.

>The interesting part is that it only happened on only one part number,
>and the board contains other  QFPs of other vendors, but no problem.
>
>Any idea ???

Yes.

Remove one of the parts with "lifted" legs, using minimal heating or simply
by desoldering the pins. Examine carefully the bottom of the plastic molded
surface, with suspicion that the surface is now rounded outward with the
dreaded popcorn disease.

If this are TQFP's (thin quad flat pack), it is a strong possibility. The
effect is that the molded plastic will swell downward, the part will then
tilt during reflow toward the edge whose leads wet first, leaving the other
edge with no contact to the paste. Some of these TQFP's have literally
paper thin plastic underneath the diepad in the belly area of the part.

Make sure the parts have been properly drypacked, stored, and that your
profile is not giving this area of the board too much heat. The ramp up
portion of the profile needs to be as gradual as possible.


regards,


Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com



***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   *
* with <subject: subscribe/unsubscribe> and no text in the body.          *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************



ATOM RSS1 RSS2