Solder pad dimensions and stencil aperture sizes for most common OTS components are listed in IPC standards such as . Suggested pad dimensions that are used in component data sheets are also loosely based on those IPC pad/aperture dimensions, to meet the solder joint requirements within IPC-A-610 and J-STD-001. All of those in turn are based on a solder paste stencil thickness of 5 or 6 mils, which is pretty much an industry standard.
But the stencil thickness also depends on the CCA design, particularly the type of CCA and the component selection and the use environment.
For example, a high-speed signal processor or data-read head driver will (generally) utilize flip-chips, fine pitch ICs, and many 0402, 0201, 00105 and yes, even smaller components. The stencil thickness could very well be optimal at .003" for this.
On the other hand, it would not be optimal for a power supply card for an under-the-hood application.
The Type of solder paste for the first may be Type 5, and for the second could well be Type 3.
So, it depends.
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Horvath, Steven
Sent: Tuesday, October 15, 2013 9:11 AM
To: [log in to unmask]
Subject: Re: [DC] Specifying max solder mask thickness
I'd specify the solder mask thickness in the notes if it's critical. As an aside, why is your solder stencil so thick? We typically use 3 mil. The thicker stencil will increase the amount of paste deposition.
Steve Horvath
SR. PCB Designer
Knowles Acoustics, Inc.
1151 Maplewood Dr.
Itasca, IL 60143
630.285.5840 (Office)
224.623.3841 (Mobile)
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-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Kitty Hines
Sent: Tuesday, October 15, 2013 8:46 AM
To: [log in to unmask]
Subject: [DC] Specifying max solder mask thickness
Good Morning,
I'm looking for the best way to specify solder mask thickness, particularly when it covers a via or pad, which causes a slight bump. This situation can cause excess solder paste on pads, after application using a
5 mil thick stencil. I've looked at the IPC-840-SM, but didn't find anything that looked like a NOTE, that I can add to my Fabrication Drawing. Or maybe I just missed it. What wording or diagram do you all use for this specification? I appreciate any help you can be.
Thank You,
Kitty
Kitty Hines
ECAD Librarian/PCB Design CID+
Chamberlain Group, Inc.
(630)516-6655 office
[log in to unmask]
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