Bob,
Nice photos.
I assume your dip paste application was on a gold pad? Do you have any experience with that material on other substrate surface finishes? Was it a lead-free application?
I built some stacked packages in a past life with a dip-paste material from a Far East paste manufacturer (are brand names allowed on this forum?). We were encouraged by the coverage of the dip and deposition, but in very limited trials, we got poor wetting. We were using an OSP finish on the substrate, and the alloy was SAC305.
I'm intrigued by the dip paste principle, especially for rework. Any information on current materials and methods would be greatly appreciated.
r.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Willis
Sent: Wednesday, June 03, 2009 12:33 PM
To: [log in to unmask]
Subject: Re: [TN] BGA-113 package
Flux can work fine in a well defined process but paste is better. However,
over the last few months of training workshops in Europe and overseas I have
been using dip paste designed for STACK Package assembly. The suppliers have
not been offering it for rework but it's a joy to use with no stencil costs,
just dip and go. I feel sure the main suppliers should offer it even at a
higher price!
With good housekeeping the material lasts a long time
Videos as always to show with some still images as well,
With flux www.smartgroup.org/pop/stack4.wmv
With paste www.smartgroup.org/pop/stack013.wmv
Dip paste images www.smartgroup.org/pop/bobwillisdippaste.gif
I cant remember if we have added some POP package defects on the Defect
Database at NPL yet but will have to check http://defectsdatabase.npl.co.uk
Many thanks
Bob Willis
2 Fourth Ave, Chelmsford, Essex, CM1 4HA England
Tel: (44) 1245 351502
Fax: (44) 1245 496123
Mobile: 07860 775858
www.ASKbobwillis.com
PCB Design for Manufacture & Assembly Workshop 15th October
www.ASKbobwillis.com
PCB Inspection & Quality Control Workshop 3rd November
www.ASKbobwillis.com/faworkshops.pdf
Book Bob's "Step by Step Failure Analysis Workshop" 4th November
www.ASKbobwillis.com/faworkshops.pdf
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Edwards
Sent: 03 June 2009 17:43
To: [log in to unmask]
Subject: Re: [TN] BGA-113 package
Steve,
I would not recommend you only use flux to reflow the BGA...
I have had to rework a lot of BGAs because someone thought that that would
be a reliable process for rigid PCBs...
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Kelly
Sent: Wednesday, June 03, 2009 9:10 AM
To: [log in to unmask]
Subject: [TN] BGA-113 package
Hi All,
We have a rigid flex that has a BGA-113 (microstar BGA) package to be
mounted to it. The routing in this area on the top layer leaves me with
.0005 of soldermask clearance from the edge of the BGA pad and .003 distance
from the edge of the soldermask to the nearest track- in other words I have
.0035 of clearance from pad edge to next track assuming a perfect etch and
perfect soldermask registration.
Having rooted around Texas Instruments web site I believe that it may be
possible to reflow this BGA without adding solder paste to the pad - just
letting the ball collapse do the attachment. If my scenario is correct I
could open up the soldermask and not have too many concerns about bridging
between the BGA pads and the tracks. Any thoughts or comments would be
appreciated.
Thanks Steve Kelly
Steve Kelly (PLEASE NOTE NEW E-MAIL ADDRESS)
(416) 750-8433 (work)
(416) 750-0016 (fax)
(416) 577-8433 (cell)
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