IPC Class 3 Annular Ring and Fine Pitch BGA Challenges

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Hello, I have a few PCB boards i am trying to be manufact... - Sep 08, 2017 by sbar5781

Any insight appreciated! ... - Sep 13, 2017 by sbar5781

I think you needed an IPC Class 3 annular ring because for v... - Oct 09, 2017 by James Barnhart

sbar5781

#78850

IPC Class 3 Annular Ring and Fine Pitch BGA Challenges | 8 September, 2017

Hello,

I have a few PCB boards i am trying to be manufactured that are miniaturized medical devices. Thus they require IPC Class 3 Specs.

However as miniature devices they have limited space, including a 0.4mm pitch BGA socket, which currently has several via-in-pads at 4/10mil sizing. They are designed currently as through holes for a mechanical drill. 4 Layer 31mil thick board.

One PCB house has informed me that due to the IPC Class 3 annular ring restriction these vias are impossible to manufacture. Hole cannot me smaller and pad cannot be larger. laser drill micro-via design are an option, at a significant cost increase and possible design adjustments on other layers.

Another PCB house has told me as they are Via-in-Pads they can be simply filled with nonconductive epoxy, and plated over. Then they are treated as typical BGA pads and the annular ring restriction will not not apply.

Which is correct?

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sbar5781

#78873

IPC Class 3 Annular Ring and Fine Pitch BGA Challenges | 13 September, 2017

Any insight appreciated!

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James Barnhart

#79148

IPC Class 3 Annular Ring and Fine Pitch BGA Challenges | 9 October, 2017

I think you needed an IPC Class 3 annular ring because for very dense designs, the smaller the annular ring the better, as less space is taken by the pad or via and more space can be dedicated to routing the traces in highly populated areas of the board. To take the annular ring constraint lower can have a greater impact on the cost when it comes to fabricating the board. The decision basically comes down to whether the benefit from greater routing space outweighs the price increase. Many designers will regularly specify a reduced annular ring constraint - happy to pay the extra cost for the freedom they have gained when it comes time to route their boards.

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