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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


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zolasteven

#21329

SMT | 27 August, 2002

Hi,

I have a few questions regarding printed circuit board.

What is the difference between the solder pads and the solder resist or mask? What is the purpose for the solder resist? What color is it? When printing solder paste should the paste be printed on following the pad configuration or resist configuration?

Thanks & rgds, Steven

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#21337

SMT | 27 August, 2002

Steven: Understand that I am not intentionally trying to create high levels of personal trauma by suggesting this ... ;-)

Please stop for just a minute, take a deep breath, think about the 'titles' that you use for your threads, and start using something other than 'SMT'. After all, this site is dripping with 'SMT' that and the next thing.

What is the difference between the solder pads and the solder resist or mask? =>

Pad. Land. A portion of a conductive pattern used as a termination area. Metal surrounding a hole on a printed circuit board. Mask. A material applied to allow selective etching, plating, or protection of the surface of a printed circuit board.

What is the purpose for the solder resist? =>

Solder Mask. Coating material used to mask or protect selected areas of a pattern from the action of an etchant, solder, or plating. Solder Mask, Dry Film. A photo-imageable dry film mask allowing a minimum 0.003 to 0.005 inch clearance on each side of the pad. Solder Mask, Liquid Photo-Imageable (LPI). LPI is the standard mask for SMT applications. It requires a clearance of 0.001 to 0.0015 inch on each side of the pad. This is very attractive for fine pitch applications, because it is a thin coating. Solder Mask Over Bare Copper (SMOBC). In printed circuit board fabrication, when the final metalization is copper with no other protective metal and non-soldereable areas are covered with a solder resist.

What color is it [solder resist]? =>

Green is the most common color of solder resist. We have boards with �red� [burgundy], tan, and brown.

When printing solder paste should the paste be printed on following the pad configuration or resist configuration? =>

Generally, most people print paste to roughly match the conductive pads. Although, there are reasons to print the paste area larger and smaller than the pad.

Look around the fine SMTnet 'Library' for 'Terms & Defintions' [er sumpin titled like thet]

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zolasteven

#21338

SMT | 28 August, 2002

Thanks for your answers

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#21348

SMT | 28 August, 2002

This all gets confusing with this jargon and that. There is a fair amount of tutorial material on the web. For instance: http://brl.ee.washington.edu/CE/notes/lec_pcb.pdf

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