TECHNET Archives

February 2005

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:
John Guy <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, John Guy <[log in to unmask]>
Date:
Mon, 28 Feb 2005 14:58:06 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (64 lines)
John,
        If I understand your problem, you are printing a 20 mil pitch component using a 6 or 7 mil thick stencil.  If this is the case, you are pushing the envelope for paste release.  Could it be that you are getting skips in the printing process?  That could easily account for any missing solder.  Also, I would not make the assumption that the solder is not going down the via.  I am currently working on a board that has a similar problem and I have seen it happen.

Hope this helps,

John Guy

 -----Original Message-----
From:   TechNet [mailto:[log in to unmask]]  On Behalf Of Mastorides, John
Sent:   Monday, February 28, 2005 2:21 PM
To:     [log in to unmask]
Subject:        [TN] Disapearing solder

Has anyone experienced solder paste disappearing in a convection oven?

We have experienced several "insufficient solder" (no solder) defects on
smt gull wing leads (typically fine pitch but not always).  The last
controlled lot, produced 3 of 10 boards with defects.  Defects: One lead
on each of 2 boards, and 3 leads on the last board.  Component types are
QFP208, TSOP48 and QFP100

Additional information:

1) The paste (6 - 7mils thick) is verified on the pads just prior to
entering the reflow oven.  The paste is a SN63 RMA.
2) Solderablity of the component leads is acceptable
3) Solderability of the board is acceptable
4) There are vias attached to every pad but the solder is not going into
the vias.
5) The defective joints exhibit a small fillet of flux around the leads
with no solder.  It appears as though solder was never printed on the
pad.  
6) The missing solder is not on the lead, pad or adjacent component
leads or pads.  It's just gone.
7) Defects found on 11 boards over 3 different lots (months apart).
8) Minute solder balls are evident on the board but may have been from
paste print process.
9) The lead is in contact with the pad.

Theories:

1) Paste outgassing??
2) Gremlins in the oven stealing the paste??

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts 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 847-615-7100 ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts 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 847-615-7100 ext.2815
-----------------------------------------------------

ATOM RSS1 RSS2