Hopefully designers provided me non-soldermask defined pads with thermal relief, good news to hear it helps.
Thank you very much for your feedback and artwork trick, I will now be able to sleep a little better this weekend.
Have all of you a nice weekend.
Regards
sylvain
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: vendredi, 19. juin 2009 15:58
To: [log in to unmask]
Subject: Re: [TN] LGA assembly question
As regular as it can be. Nothing special in handling them.
Just a couple of DfM recommendations, though:
Instead of having all those solder mask defined pads right on the Cu plane, as recommended by Linear, I had the pads designed non-solder mask defined, with thermal connections to the plane. This reduces that thermal demand.
The placement of the components is impossible to visually inspect before reflow, add corner chevrons in the artwork
Salutations,
Ioan Tempea, ing.
t : 450-967-7100 ext : 244
[log in to unmask]
www.digico.cc
P N'imprimer que si nécessaire - Print only if you must -----Message d'origine----- De : Sylvain Kaufmann [mailto:[log in to unmask]] Envoyé : 19 juin 2009 09:49 À : [log in to unmask] Objet : [TN] LGA assembly question
Ioan,
Merci pour le retour.
One question more if I may: did you set a different placement force as you would have used for a BGA for example, or did "regular" setting work well?
Bev, sorry I answered your question personnaly, I sent my reply too quickly. To sumarize for others, in my mind QFN are packages with a ground/thermal plane in middle and signals connection in periphery. And LGA is like a BGA but with square pads and no balls.
I am concerned about shorts because this device is a DC/DC that can drive up to 12 amps and I would not see these assemblies burn because of assembly issues.
Thank you again
Regards
sylvain
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: vendredi, 19. juin 2009 15:16
To: [log in to unmask]
Subject: Re: [TN] LGA assembly question
Bonjour Sylvain,
I have recently done several boards with the exacly same components, in almost the same conditions as yours. I had ENIG/Pick'n'place/lead-free SAC305. The only difference was I did convection reflow.
They print well, they solder well. I would not dread shorts, this package is more lenient than QFNs. The only 2 special things I have observed were:
- The thermal demand is higher than for regular BGAs. I had metal top BGAs on the same board, still the LGAs were 10 deg C colder. In order to bring the LGAs at 240deg C I had to bump the BGAs up to 250 deg C.
- Hard to control voiding
Since I am not familiar with vapour phase, maybe the above will not be an issue for you.
Regards,
Ioan Tempea, ing.
t : 450-967-7100 ext : 244
[log in to unmask]
www.digico.cc
P N'imprimer que si nécessaire - Print only if you must -----Message d'origine----- De : Sylvain Kaufmann [mailto:[log in to unmask]] Envoyé : 19 juin 2009 09:06 À : [log in to unmask] Objet : [TN] LGA assembly question
Dear Technetters,
Our assembly workshop has to assemble 4 prototype boards where LGA packages with 133 connections are used. I allready worked with BGAs or QFNs but never with LGA packages and I am concerned about shorts/open that could occur.
Provided that I cannot run tests and conditions are as followed:
- ENIG surface finish boards
- Vapor phase reflow soldering
- Pick and Place machine
- Leadfree or lead containing solder can be used
Would some of you be kind enough to share experiences/advices so that we would have little chances to successfuly assemble these boards?
Thank you in advance for your help.
S. Kaufmann
************************************************************
Sylvain Kaufmann
CERN / European laboratory for particle physics Site de Meyrin
1211 Geneva 23
Switzerland
Dpt: EN-ICE-DEM (int mail J06600)
Phone: +41 22 767 37 02
Fax: +41 22 766 87 77
E-mail: [log in to unmask]
Web: www.cern.ch
http://cern.ch/dem
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