TECHNET Archives

July 2009

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:
Bev Christian <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Bev Christian <[log in to unmask]>
Date:
Fri, 10 Jul 2009 11:49:00 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (191 lines)
Syed,
Thank you so much. Since Technet doesn't give color, I will answer in
caps, but I am not yelling. :)

Bev
RIM

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Syed Ahmad
Sent: Friday, July 10, 2009 11:41 AM
To: [log in to unmask]
Subject: Re: [TN] More Underfill Discussion

Just to keep in mind whether it applies directly to the situation under
discussion or not,

1. It is quite possible and probable to develop a void-free process, so
the
consideration of voided material acceptance should be an exception and
not a
norm.
- IN AN IDEAL WORLD

2. Voids always have the potential to cause problems whether reported in
the
literature or not.
- AGREE

Below are comments from a coworker here who is a reliability person:

<<
I think it's pretty well understood that if you have significant voiding
around underfilled solder joints the solder will extrude into the void
under
temperature cycling. The joint shape thus becomes distorted, and the
degree
of distortion depends on the size and shape of the void and the number
of
cycles imposed.
- AND THE TEMPERATURES OF THE CYCLING REGIME.

Distorted solder joints are less reliable than pristine,
barrel-shaped joints due to stress concentrations.
-AGREE

I doubt that in a high-reliability application space that any customer
would
accept even 50% voiding around a joint, much less a void spanning two
joints.
- DEFINE HIGH RELIABILITY IN THIS CONTEXT.

Standoff heights of 100 microns or more can be underfilled without
voids;
this is not difficult with a little process development. BGA joints are
roughly that size or larger, but flip chip are often smaller, of course.
Defining a good dispense pattern for flip chip or BGA is often a black
art
that takes some experimentation in the lab, as you know.
- EVEN MORE OF A BLACK ART IF YOUR DESIGNERS WON'T ALLOW HOLES IN RF
CANS!
>>

He was with Motorola for a number of years and got the following
comments
from there:

<<
My amigo at Freescale tells me they generally subscribe to a JEDEC C-SAM
inspection standard for flip chips.
- C-SAM DOESN'T WORK FOR MULTI-LAYERED BGAs THOUGH

The standard states something like no
more than 5-10% total die area can be void, with NO voids allowed in the
last row of joints at the die edge (since they fail first in temp cycle
and
drop). He couldn't remember if the actual number was 5% or 10%.

He is not aware of a similar standard for BGA joints, but they apply the
same 5-10% rule with no voids allowed at die edge or package edge (where
failures occur first).
- THIS IS EXCELLENT INFORMATION!!

He thought the JEDEC standard might be free, if you're interested.
>>

My personal experience is that a void free process can be developed and
that
in flip chips voids cause stress at the edges and chip damage is
possible at
the edges of the void.
-AGAIN I AM TALKING CSPs AND BGAs, NOT FCs.

Chip damage also is possible when the edge of the
chip is covered partially.
-AGREED
Bev
RIM

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Thursday, July 09, 2009 3:10 PM
To: [log in to unmask]
Subject: [TN] More Underfill Discussion

TechNetters,
Well I have been shopping to Class 2 people the draft we all built here
on TechNet of a standard for underfill workmanship. Some are saying
they can't live with voids that only go 50% around the perimeter of a
solder ball, they want more leeway. They also say they want to allow
voids connecting solder balls. Now I put in the prohibition of the
latter because of the statement in the J-STD-030 "Guideline for
Selection and Application of Underfill Material for Flip Chip and Other
Micropackages", where it talks about unequal stresses put on the solder
balls when they is not 100 underfill coverage around each and every
ball. My questions to you are:
1) What is the physical evidence behind that statement in 030?
2) What was the magnitude of the deformation?
3) How long did it take?

My reason for the last question is if it takes 9 years for significant,
reliability impairing deformation to occur in a 20 year life product,
that is real bad. But if it happens in the products with a 2 to 3 year
life product, why should we care?

Bev
RIM


---------------------------------------------------------------------
This transmission (including any attachments) may contain confidential
information, privileged material (including material protected by the
solicitor-client or other applicable privileges), or constitute
non-public
information. Any use of this information by anyone other than the
intended
recipient is prohibited. If you have received this transmission in
error,
please immediately reply to the sender and delete this information from
your
system. Use, dissemination, distribution, or reproduction of this
transmission by unintended recipients is not authorized and may be
unlawful.

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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 15.0
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
-----------------------------------------------------

---------------------------------------------------------------------
This transmission (including any attachments) may contain confidential information, privileged material (including material protected by the solicitor-client or other applicable privileges), or constitute non-public information. Any use of this information by anyone other than the intended recipient is prohibited. If you have received this transmission in error, please immediately reply to the sender and delete this information from your system. Use, dissemination, distribution, or reproduction of this transmission by unintended recipients is not authorized and may be unlawful.

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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