Dave,

Interesting calculation.  I have never seen the numbers worked out.  Is this
calculation and your ratio documented in a reference book or something?
Does the formula also apply to BGAs?

Some of our new designs have BGAs on both sides which I am evaluating.

Look forward to your reply.  thanks

joe

-----Original Message-----
From: David Fish [mailto:[log in to unmask]]
Sent: Monday, June 30, 2003 1:38 PM
To: [log in to unmask]
Subject: Re: [TN] Double-sided reflow with Altera RQFP...



Hi Steve


We don't double reflow this part. We wouldn't consider it without a fixture
or some other support.


You know that sound, the almost involuntary sound that patrons in a
restaurant make when a waiter drops a glass or a tray? It's kind of an
"oooooo" sound. Well if you run these parts, the sound that the troops at
your plant will make will be so loud as those pups start Peter Panning to
the floor that the people in the front will stop playing games on the
computer and walk out back to find-out what's going on.


Do the numbers:
* Part weight: 15.1 gm
* Lead toe to heel: 0.46/0.66 mm
* Lead width: 0.17/0.27 mm


Lead wetting area = 240* [0.46*0.17] mm^2 = 18.7 mm^2 [0.03inch^2]
Weight of component to total pad mating area ratio: 15.1 gm / 18.7 mm^2 =
804.6 mgm per mm^2 [519.1 gm per inch^2]


A commonly acceptable ratio is: 50 mgm per mm^2 [30 gm per inch^2]
Pushing the boundary ratio is: 44 gm per inch^2

Dave Fish

----- Original Message -----
From: Steve Gregory <mailto:[log in to unmask]>
To: [log in to unmask] <mailto:[log in to unmask]>
Sent: Monday, June 30, 2003 8:42 AM
Subject: [TN] Double-sided reflow with Altera RQFP...

Mornin' All!

Just a quick question, has anybody ever done a double-sided reflow with a
240-pin Altera RQFP on the bottom that has a metal heatsink in the top?

Thanks!

-Steve Gregory- ---------------------------------------------------
Technet Mail List provided as a free 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/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
-----------------------------------------------------


---------------------------------------------------
Technet Mail List provided as a free 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/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a free 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/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------