SMD (Solder Mask Defined) and NSMD Pads

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   Hi Tom:

I know BGA land pattern design have two method, SMD(solder mask defined) and NSMD (non-solder-mask-defined), NSMD will be good than SMD for BGA pad to increase solder joint reliability. 

What about other components? chip, sop, connector and etc. 

Is NSMD also priority option for most components? 

Is there any related description in IPC/JEDEC standard? 

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drj-bbe Members Profile Send Private Message Find Members Posts Add to Buddy List Advanced User Joined: 08 Jul 2015 Status: Offline Points: 71	Post Options Post Reply Quote drj-bbe Report Post Thanks(0) Quote Reply Topic: SMD (Solder Mask Defined) and NSMD Pads Posted: 24 Sep 2015 at 5:45pm
	Hi Tom: I know BGA land pattern design have two method, SMD(solder mask defined) and NSMD (non-solder-mask-defined), NSMD will be good than SMD for BGA pad to increase solder joint reliability. What about other components? chip, sop, connector and etc. Is NSMD also priority option for most components? Is there any related description in IPC/JEDEC standard?



Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5716	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Posted: 24 Sep 2015 at 9:36pm
	BGA pad size and solder joint relation is totally different than Chip, SOP and Connectors. The NSMD BGA pad stack is necessary for the Ball to fully collapse around the pad edge securing it to the PCB - The SMD (Solder Mask Defined) BGA pad stack prevents the Ball Collapse - The BGA ball melts during reflow and other component leads do not.
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drj-bbe Members Profile Send Private Message Find Members Posts Add to Buddy List Advanced User Joined: 08 Jul 2015 Status: Offline Points: 71	Post Options Post Reply Quote drj-bbe Report Post Thanks(0) Quote Reply Posted: 24 Sep 2015 at 10:26pm
	So, which method will be better for PCB land pattern soldered BGA? I have seen a describtion in IPC-7093 6.1.3.6 solder mask design. NSMD is better than SMD on QFN solder joint strenth. Should I assume that NSMD is first option for other chip, sop and connectors. What about your opinion?

Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5716	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Posted: 25 Sep 2015 at 5:20am
	NSMD is normally used on every SMT pad due to registration tolerance of +/- 0.05 mm. You do not want any solder mask on the pad so the minimum solder mask opening should be 0.05 mm. The exception to this rule is Flexible Circuit libraries normally have a 0.05 mm solder mask over the Toe and Heel of the pad to act as an epoxy glue to hold the pad down while flexing the board.
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