Hi, Andy
We have designed many boards with fine pitch (20 and 25 mil) SMT and
have always used a continuous window around the lands on each side of
the package (no soldermask between lands) for the fine pitch parts. As
far as I know, the lack of soldermask between the lands does not make
bridging worse. We typically use a land width of .012 for .020 pitch and
a land width of .015 for .025 pitch. You need about .002 to .003 land to
soldermask clearance per land side, so the soldermask web width between
lands would be small to non-existent. You should talk to your assembly
house about this. I think they would rather have no soldermask than a
very thin web. I would like to get some responses from some assemblers
about this.
Nick Wander
Unisys, Roseville, MN
>----------
>From: Andy[SMTP:[log in to unmask]]
>Sent: Thursday, March 13, 1997 6:18 PM
>To: Wander, Nicholas G
>Subject: RE: Solder Mask on fine pitch SMT component
>
>Hi Nick, if I place a soldermask window across the SMT pads, will they have
>solder-bridge during reflow / wave soldering process? This may jeopardize my
>process. If this is inevitable, pls advice me what I can do to minimize them.
>
>Thanks
>
>Andy Tan
>
>
>-----Original Message-----
>From: Wander, Nicholas G [SMTP:[log in to unmask]]
>Sent: Thursday, March 13, 1997 10:52 PM
>To: 'Technet'; 'Andy'
>Subject: RE: Solder Mask on fine pitch SMT component
>
>Andy, we normally do not put solder mask between surface mount pads on
>20 and 25 mil pitch. We just have a continuous window around all the
>pads on each side of the part. You really do not need solder mask
>between the pads as long as there are no traces between the pads.
>
>Nick Wander
>Unisys, Roseville, MN
>
>>----------
>>From: Andy[SMTP:[log in to unmask]]
>>Sent: Wednesday, March 12, 1997 7:38 PM
>>To: 'Technet'
>>Subject: Solder Mask on fine pitch SMT component
>>
>>Hello
>>
>>I am facing a problem with fine pitch SMT component of 20mils. How can the
>>soldermask be applied in between the pads without covering them? My supplier
>>claims that their process capability is restricted.
>>
>>Another Question:
>>Which PCB manufacturing house in Singapore can produce 6mils trace/air-gap
>>(for internal layers as well) specifications?
>>
>>
>>Please Advice...Thanks
>>
>>
>
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