Awhile back I posted a detailed response on this subject, but don't have the time today to repeat it here. But basically, there is only so much room for solder paste to wet out on a chip cap or chip resistor: the pads and the endcaps. Solder will only flow about halfway up the endcaps, and if there is enough molten solder still on the pad, it has nowhere to go but off the pad, hence the formation of solder balls. Don't ask me why they like to roll to the mid-chip location, but they do.
So it stands to reason that you may not see them when using a 4-mil stencil, as you are now putting a little less paste on, but not too much.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, May 01, 2012 2:46 PM
To: [log in to unmask]
Subject: Re: [TN] Homeplates on 4 mil thick stencils?
Hi Phil,
Yep. Most of the time it's either 4 or 6 mil. Once in a while I'll order a 5-mil. I find it interesting that nowdays that what I consider my "thick"
stencils are only 6-mils thick. It doesn't seem like it was that long ago that my two favorite thicknesses was 8 and 10-mil.
I don't homeplate much at all. Have never really needed to since I've always used water soluble paste and we clean everything we build. Have I seen mid-chip solder balls with 5 and 6-mil stencils, you bet. But it's been my observation that with 4-mil stencils I don't see mid-chip solder balls. I also asked others here just in case I was going blind, and they said that they don't see them either...TIFWIW
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro
Sent: Tuesday, May 01, 2012 3:33 PM
To: [log in to unmask]
Subject: Re: [TN] Homeplates on 4 mil thick stencils?
I only have mild experience with 4 mil stencils.
Steve,
I assume you have used 5 and 6 mils as well. Is it correct to assume that
you never homeplated those designs either?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: Tuesday, May 01, 2012 10:47 AM
To: [log in to unmask]
Subject: Re: [TN] Homeplates on 4 mil thick stencils?
Dear Technos,
I see questions towards Steve, does this mean you use 4 mil stencils and your experience goes against his? Should I take this as 4 mil would create mid-chip balling without homeplating because you've seen it, or it is rather technical curiosity?
Thanks,
Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer T |
450.967.7100 ext.244 E | [log in to unmask] W | www.digico.cc
N'imprimer que si nécessaire - Print only if you must
-----Message d'origine-----
De : Phil Bavaro [mailto:[log in to unmask]]
Envoyé : May-01-12 1:28 PM
À : [log in to unmask]
Objet : Re: [TN] Homeplates on 4 mil thick stencils?
Steve,
I would check your wrap around termination capacitors. There are many ways
to skin that cat and I suspect your paste aperture is already less than 1-to-1.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, May 01, 2012 7:28 AM
To: [log in to unmask]
Subject: Re: [TN] Homeplates on 4 mil thick stencils?
Hi Richard,
I just looked closely at some product that we were running today that's using a 4-mil stencil (with no homeplates), and I don't see any mid-chip solder balls, and I looked at where they would most likely occur if there were to be any:
http://stevezeva.homestead.com/4-mil_no_homeplate.JPG
I can't say that we NEVER have any, sometimes it happens, like when the wrong sized part is used on a footprint designed for something else (oh wait, that never happens!). But overall, usually don't see them when we use a 4-mil thick stencil.
Steve
-----Original Message-----
From: Stadem, Richard D. [mailto:[log in to unmask]]
Sent: Monday, April 30, 2012 3:56 PM
To: TechNet E-Mail Forum; Steve Gregory
Subject: RE: [TN] Homeplates on 4 mil thick stencils?
Steve,
Somewhat related to the other discussion on cleaning of no-clean:
Do you wash the assemblies after reflow, and is that why you do not see any mid-chip solder balls?
Do you wash any CCAs that have been processed with a no-clean solder paste or no-clean wire solder?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, April 30, 2012 2:42 PM
To: [log in to unmask]
Subject: Re: [TN] Homeplates on 4 mil thick stencils?
BTW I forgot to add I don't homeplate anything...
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, April 30, 2012 3:16 PM
To: [log in to unmask]
Subject: Re: [TN] Homeplates on 4 mil thick stencils?
Hi Ioan,
We use 4-mil thick stencils quite often and I don't see mid-chip balling...
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: Monday, April 30, 2012 2:54 PM
To: [log in to unmask]
Subject: [TN] Homeplates on 4 mil thick stencils?
Dear Technos,
It is my first 4 mil stencil and I was wondering if mid-chip balling is still an issue at this thickness (no-clean process). Should I still homeplate the apertures of passives, as I fear insufficient solder?
Thanks,
Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer T |
450.967.7100 ext.244 E | [log in to unmask] <mailto:[log in to unmask]> W | www.digico.cc <http://www.digico.cc/>
N'imprimer que si nécessaire - Print only if you must
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