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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Criteria for Min Thickness regarding Large and Small pads

Views: 1755

#55116

Criteria for Min Thickness regarding Large and Small pads | 18 June, 2008

Does anyone know of an established guideline for thickness requirements? Our smaller pads continue to receive a thicker solder deposition when we measure by the larger pads for process accessibility and vice versa for the larger pads when we measure by the smaller ones.

reply »

#55142

Criteria for Min Thickness regarding Large and Small pads | 19 June, 2008

Please give us more information about the source of the solder that you mention. Is it: * HASL applied by your supplier * Solder on pads after wave soldering * Solder paste after printing * Solder on pads after reflow soldering

... or what?

reply »

#55284

Criteria for Min Thickness regarding Large and Small pads | 29 June, 2008

I was referring to the HASL supplied by the supplier...specifically Lead Free HASL. I've been searching the web and I cannot find a thickness specification like we have for ENIG and Immersion Silver.

reply »

#55288

Criteria for Min Thickness regarding Large and Small pads | 30 June, 2008

It will be tough to find a dimensional thickness specification for HASL. IPC-6012 Table 3-2, line "Fused tin-lead or solder coat - Coverage and Solderable" states the requirement that there has to be complete coverage of solder on the land, and it must be wettable.

If you want uniform solder thickness with HASL, you should make all the pads the same size. Any HASL thickness: * Less than 2 micron has a limited shelf life * Above 5 micron has a long shelf life of over a year with reasonable storage conditions

For more on HASL thickness: * Part of an University of Bolton online course here: http://www.ami.ac.uk/courses/topics/0142_cftl/index.html

* Check Sherry Goodell's Chapter 30 of "Printed Circuits Materials Handbook", for lots of info about the HASL coating and it's specifications here: http://www.goldphoenixpcb.biz/pdf/Chapter_30-HAL.pdf

reply »

Manufacturing Software

 Reflow System