TECHNET Archives

June 2008

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:
Ryan Grant <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Mon, 30 Jun 2008 15:07:36 -0600
Content-Type:
text/plain
Parts/Attachments:
text/plain (172 lines)
Wow!  So this suggest a big CTE mismatch between the top side components
and the PCB.  Once the solder freezes, shrinkage of the PCB is greater
than the BGA.  It sounds like you're straight out of luck :(

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ted Kong
Sent: Monday, June 30, 2008 2:59 PM
To: [log in to unmask]
Subject: Re: [TN] Bow PCAs

Hi Ryan,


I did run the board through with the narrower side.  The interesting
thing is that the board bowed upward.    When I run the blank boards
through twice, I don't see any bowing.  I will consider the stiffeners
if I can remove it the bow from other means.  

Thanks for everyone's reply.

Ted


--- On Mon, 6/30/08, Ryan Grant <[log in to unmask]> wrote:

> From: Ryan Grant <[log in to unmask]>
> Subject: Re: [TN] Bow PCAs
> To: [log in to unmask]
> Date: Monday, June 30, 2008, 12:35 PM
> Hi Ted,
> 
> The bowing is due to the weight of the heatsink/BGA combo. 
> 
> 
> By 175C, your boards are sure to have reached their glass
> transition
> temperature, which means, even though the board is still a
> solid, it is
> soft and malleable and can easily be distorted.  The weight
> of the
> heatsink/BGA combo is causing the board to sag between the
> oven rails.  
> 
> Rotate the board 90 degrees through reflow and the bowing
> should go
> away.  4 inches is usually the minimum conveyor rail width,
> so you are
> in luck, your board will still fit.
> 
> If you don't think rotating the board is an option,
> your other
> alternative is Titanium board stiffeners that must be
> attached before
> reflow and removed afterwards.
> 
> Thanks,
> Ryan
> 
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Ted
> Kong
> Sent: Monday, June 30, 2008 1:24 PM
> To: [log in to unmask]
> Subject: [TN] Bow PCAs
> 
> Hi Technetters,
> 
> I have a 14.5" x 4" PCB that bows after top side
> reflow.  I haven't
> measure the actural bow amount yet, but it looks like it
> will meet IPC
> spec.  However, I want to see what I can do to eliminate
> it.  
> 
> I run a blank board through the same reflow profile and
> don't see any
> bowing.  The production boards do not have any bowing after
> bottom side
> reflow.  Bowing only occur after the top side reflow.  I
> believe the
> bowing is due to the two 40mm2 BGAs on the board, which is
> located 4"
> from the long edge (center from the narrow width).  Both
> BGAs have large
> heat-sinks attached to them.  I reflowed three additional
> boards on a 10
> zone reflow oven (instead of a 7 zone) oven, but didn't
> see any
> improvements.  Can anyone give me any other suggestion on
> how to
> eliminate the bowing?  Is my assumption of the cause
> correct?
> 
> Thanks all in advance.
> 
> 
> Ted 
> 
> 
>       
> 
> ---------------------------------------------------
> 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
-----------------------------------------------------

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