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Solder mask between pins of 32u4?
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Solder mask between pins of 32u4?

by vputz on Thu May 02, 2013 6:21 am

I'm having solder-bridge problems between the pins of my 32u4 processors when I reflow them, and noticed that the footprint I was using in KiCad (which I think was auto-converted from the 32u4bb Eagle files) doesn't have solder mask between the pins of the 32u4. Discussing this with folks, some think the solder mask should be there, others think that for QFP it's fine enough that it's problematic. What do most people do?

vputz
 
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Joined: Mon May 03, 2010 5:43 am

Re: Solder mask between pins of 32u4?

by alphatronique on Thu May 02, 2013 1:19 pm

Hi

first plase refer to footprint calculator of IPC 7351A pcblibraries.com for see if pad was right size (free calculator)

normally solder mask was 1:1 whit pad and PCB shop increase it of ~2 mil if need

some shop have obsolete equipment and remove mask bethen 0.5mm pitch IC ,so stay far from it

but if you not have solder mask bethen pin you will more prone to solder bridging

it may also solder past volume issue ,normally past was 10 -20 % shrink from pad for 5 mil think stencil
whit that normally it was fine if your process was good

so solder mask permit to increase your yield or process variation

a+
Best regard
Marc Lalonde CID.
IPC Certified PCB Designer.
Alphatroniqe inc.
www.alphatronique.com
http://ca.groups.yahoo.com/group/MyData_Group

alphatronique
 
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Re: Solder mask between pins of 32u4?

by vputz on Thu May 02, 2013 6:25 pm

Good points. I hadn't actually registered that solder mask was calculated based on design rules rather than part of the footprint; I probably have conservative design rules since earlier I was using them for my minimill. I'll take a closer look when I make my next prototypes.

vputz
 
Posts: 64
Joined: Mon May 03, 2010 5:43 am

Please be positive and constructive with your questions and comments.