Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Land Pattern Discrepencies

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Land Pattern Discrepencies | 25 March, 2006

Hi everyone, I'm relatively new to SMT PCB design and am running into some frustration with the land pattern design of "standard" smt components in particular passive chip components. It seems each manufacturer (Yageo, Rohm, Panasonic) has their own spec for pad layout and IPC seems to have yet another. My CAD package then has it's own and they are all relatively close...but all different. Being new I've tried to go by manufacturer data sheets for most of the special stuff like PowerDI-5, SuperSOT-6, and even SMA and SMB diode packages. But there are a ton of chip caps and resistors I need placed and the BOM gives a number of different manufacturers. How do I handle this? Is there a guide somewhere?

Thanks, Rob

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Land Pattern Discrepencies | 27 March, 2006

Design to IPC standards unless a supplier provides documentation on why a change to the standard was necessary. Throw all supplier data sheets in the trash.

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Land Pattern Discrepencies | 28 March, 2006

Hi Rob,

They want you to think that their products are subtly different & that they are not interchangeable, although they are in nearly all cases (this is different for high frequency RF design).

Also your layout guys aren't going to love you with a plethora of footprints for each case size, depending on manufacturer. Follow Dave's advice & go with IPC, then you can't go wrong. Although, keep an eye out for anomoly parts such as resistor networks that can be concave or convex, and tants, where on larger sizes people like Kemet & AVX mix up their case size codes.



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