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February 2004

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Subject:	Re: Regarding Solder Mask Preference
From:	Roger Stoops <[log in to unmask]>
Reply To:	(Designers Council Forum)
Date:	Mon, 2 Feb 2004 09:37:53 -0500
Content-Type:	text/plain
Parts/Attachments:	text/plain (64 lines)

Oommen,

Sometimes this depends on who you talk to.

Some board vendors will tell you they want gang mask for fine-pitch parts.  It allows for easier production of the bare board.

Some assembly vendors however will tell you that they want individual mask for each pad, to improve manufacturability of assembly.  It helps reduce solder shorts between pads, therefore reduces rework.

It would be best to find out what your assembly house requires.  It would probably be less expensive for the board vendor to use individual mask openings versus the assembly vendor having to rework board after board because the gang mask allowed solder bridging.  Then ask the board house what they can do for you.  A 3-4 mil solder mask dam is about as small as they like to go, with a 2 mil gap between mask and pad.  Sometimes they will/can make the gap even smaller.

Best Regards,

Roger M. Stoops, CID+
Trimble Navigation Ltd., Dayton, OH, USA
Ph: +01 937.245.5288
Fax: +01 937.233.7511


-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]]On Behalf Of
Oommen Mathews
Sent: Monday, February 02, 2004 8:26 AM
To: [log in to unmask]
Subject: [DC] Regarding Solder Mask Preference


Hi.,


    For fine pitch QFP and SOP components (.5 mm or less) which type of solder mask is preferred in a fab point of view ? Gang solder mask or individual pin/pad mask ?


regards,
Oommen Mathews

----------------------------------------------------------

Sr. Engineer - VLSI/System Design,

Wipro Technologies Global R & D,

Tower-4/First Floor/Wing-A,

#72, Keonics, Electronics City,

Hosur Main Road,

Bangalore - 560 100. India

Tel:+91 (0)80 8520408 Ext:4132

Res:+91 (0)80 6659004

email: <[log in to unmask]>

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