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What is the preffered spacing between PTH and SMT pads

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#58660

What is the preffered spacing between PTH and SMT pads | 27 April, 2009

Can someone point me to a standard, if there is any, or design rule regards with preffared spacing between PTH and SMT pads for LF wave soldering process (SAC alloy)

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ETS

#58665

What is the preffered spacing between PTH and SMT pads | 28 April, 2009

There's a nice tool on this site - http://www.enhancetechnical.co.uk/

Click on Internet Tools and then the image - brings up a useful interactive tools which helps understand influences on wave solder bridges.

Dave

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#58666

What is the preffered spacing between PTH and SMT pads | 28 April, 2009

When using high tin solder, doesn't proper specing to avoid the effects of tin whiskers become at least as large an issue as proper specing for defect-free wave solder processing?

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ETS

#58674

What is the preffered spacing between PTH and SMT pads | 29 April, 2009

It depends on the application what will be considered the biggest issue to avoid (production or longterm reliability). Tin Whiskers are bit of an unknown quantity - but a more realistic problem could be dendritic growth / electromigration forming shorts. This depends on flux residues, moisture, voltage, conformal coating, etc.

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#58687

What is the preffered spacing between PTH and SMT pads | 30 April, 2009

Thanks for the info so far, but still need a number or a formula to calculate. The site you have point me to can support in a way, but if I want to release a design procedure to our editors, a number will be very helpful. One more issue is what can be consider as a minimum space between selective wave soldering pallet's opening to the nearest PTH or SMT pad? is there a rule of thumb to this one too?

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ETS

#58688

What is the preffered spacing between PTH and SMT pads | 30 April, 2009

Michael, There are so many factors involved that mean a definitive number is extremely difficult - if not possible.

I recommend you speak with Tony Wilson. He has been in the industry for over 25 years and reccently done PhD work on modeling failuremodes in electronics assembly. A.R.Wilson (at) lboro.ac.uk

Alternatively - there are many individuals out there (myself included) that offer DFM (design for manufacture) services.

Regards, Dave

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#58689

What is the preffered spacing between PTH and SMT pads | 30 April, 2009

Thanks , I'll try it too.

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#58702

What is the preffered spacing between PTH and SMT pads | 30 April, 2009

Selective Wave Soldering DoE to Develop DfM Guidelines for Lead and Pb-Free Assemblies Written by Makram Boulos, Craig Hamilton, Mario Moreno, Ramon Mendez, German Soto and Jessica Herrera Circuits Assembly Magazine, 31 December 2008 19:00 The minimum PTH-to-SMT pad-to-pad spacing for SAC 305 cannot be less than 0.250" without a significant rise in barrel-fill defects.

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#58704

What is the preffered spacing between PTH and SMT pads | 1 May, 2009

Manufacturing Software

Boundary Scan