TECHNET Archives

August 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:
Mike Sewell <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Mike Sewell <[log in to unmask]>
Date:
Tue, 11 Aug 2009 07:32:13 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (221 lines)
We wound up going 1 to 1 (of the part pad dimension) on the I/Os and a
50% reduction (of the PCB pad, which was smaller than the part pad) in a
4 x 4 grid on the thermal pad.  The vias were closed on the thermal pad.
4mil stencil and type 4 paste, 63/37.  We started with Actel's
guidelines and got marginal results. Didn't want to go to a 4 mil
stencil but the area ratio was better, tried an overprint with a 5 mil
but got bridging...lots of fun. Virtually no standoff but the x-ray
looked okay and boards passed test. 

Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tan Geok Ang
Sent: Monday, August 10, 2009 7:43 PM
To: [log in to unmask]
Subject: Re: [TN] Actel QFN180 Assembly

BTW. I am using Sn/Pb if using Pb-free the thermal pad opening has to be
even lesser. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne - IIW
Sent: Monday, 10 August 2009 9:49 PM
To: [log in to unmask]
Subject: Re: [TN] Actel QFN180 Assembly

I haven't tried to put down this part, but I did want to share my simple
rule of thumb for stencil design for QFN pads:

Make the thermal pad look as much like the I/O pads as possible:  Use a
grid of deposits which are about the same size and overall density as
the I/O pads.  Probably for this part that will make the thermal
significantly less than 50%, but often not much is needed.  I usually
end up potting almost everything we produce, so I can count on heat
getting out through the potting material.

Wayne Thayer

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of stephengregory5849
Sent: Monday, August 10, 2009 9:39 AM
To: [log in to unmask]
Subject: Re: [TN] Actel QFN180 Assembly

I can tell you that the application note that Actel puts out for their
QFN180 is worthless. The reduction for the thermal pad that GA Tan is in
the
ballpark, might even be a little too much. The problem with this part is
that there is such a razor thin balance between figuring out how much
paste
you print for the thermal pad and getting decent I/O pad joints. The
three
row I/O pad pattern make things all the more difficult. We were dealing
with
single and double row QFN's without any problems until we ran across
this
beast.

Oh, as far as trying to rework the part, good luck! It ain't happening.
We
even paid a company who does nothing but rework for a living to try and
rework the part and it gave them fits. They were able to get the part
back
down after much difficulty, but the board never worked. Don't know if
the
part died during rework or if it was something else. Just know it
wouldn't
program when we got the boards back.

Steve

----- Original Message -----
From: "Tan Geok Ang" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, August 10, 2009 2:24 AM
Subject: Re: [TN] Actel QFN180 Assembly


Hi Grivon,
               There is some guide from Actel :
http://www.actel.com/documents/QFN_AN.pdf which I don't think it will
work
well. Go for a volume of 55% at the thermal pad (and a pad opening of
9mils
(5mils stencil thickness) with slight rounded radius at the corner of
the
opening. What is your problem and stencil openings? With your result,
you
will able to know where gone wrong. FYI, we used only two rows of QFN as
of
now and lots of LGAs. Hope it help.

Regards
GA Tan

________________________________

From: TechNet on behalf of GRIVON Arnaud
Sent: Fri 8/7/2009 6:04 PM
To: [log in to unmask]
Subject: Re: [TN] Actel QFN180 Assembly



Coming back on an old post from Steve (at his former employer...).
Does anybody have good stencil rules for the assembly of multi-row QFNs
and
especially triple-row such as ACTEL QFN180?
Like Steve and probably many others, we tried to find the right aperture
balance between I/Os and central thermal pad without success...
A. Grivon

---------------------------------------------------
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
-----------------------------------------------------

---------------------------------------------------
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 e-mail and any files transmitted with it may be proprietary and are
intended solely for the use of the individual or entity to whom they are
addressed. If you have received this e-mail in error please notify the
sender.
Please note that any views or opinions presented in this e-mail are
solely those of the author and do not necessarily represent those of ITT
Corporation. The recipient should check this e-mail and any attachments
for the presence of viruses. ITT accepts no liability for any damage
caused by any virus transmitted by this e-mail.

---------------------------------------------------
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
-----------------------------------------------------

---------------------------------------------------
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