Jack Olson wrote:
>Jim Williams wrote:
>>
>>      Some designers make an effort to maintain a web of soldermask between
>>      the solder pads on SMT devices, where pad spacing permits. When the
>>      spacing of fine pitch devices preclude the web, it is omitted. I have
>>      heard that the webs are used to reduce solder bridging.
>>
>>      Thinking through this issue, I find webs being used where pad spacing
>>      is large enough so as to make solder bridging unlikely, while webs are
>>      omitted when the pad spacing is close enough to make solder bridging
>>      most likely.
>>
>>      I am interested in any factual data that supports the reason for, or
>>      the value of, soldermask webs.
>
>
>...don't have any factual data for you, but here's one comment:
>
>I would think the greatest benefit of soldermask webs is during wave
>soldering, and many mixed-technology boards are still wave-soldered, right?
>But from my experience most fine-pitch assemblies use reflow and solderpaste,
>so a soldermask web is of little value. In fact, very thin webs between
>fine-pitch parts can just crack and flake off under high heat, so what's the
>point? Anyone disagree?
>                                                        Jack
>

Disagree, for my shop.

We often hand or bar solder fine pitch componets, during a repair or right
from the start.  The solder mask webs reduce the occurance of little dross
shorts under the component.  This is no where near the most high tech
assembly shop in the world, but it is typical of small quantity assembly
technics.


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