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Subject:	PWB Layout spacing queries
From:	prashant chopra <[log in to unmask]>
Reply To:	TechNet E-Mail Forum <[log in to unmask]>, prashant chopra <[log in to unmask]>
Date:	Wed, 21 Oct 2009 05:36:41 -0700
Content-Type:	text/plain
Parts/Attachments:	text/plain (32 lines)

Hi,
I have a couple of queries with regard to the component spacing ---
1. What should be the minimum spacing between the QFP and the nearest chip components? (Assuming that the in case of failures the QFP will be reworked manually using the soldering iron).
2. What should be the minimum spacing between the QFN package and the nearest chip component? ( I am attaching a datasheet of QFN above).
3. What should be the minimum spacing between the 0402 component and the other nearest 0402 component or chip component?
Also, I have one query reagrding the QFN rework process (datasheet attached above) --
1. Ideally, in case of replacing the old QFN, the rework procedure should be similar to the BGA rework procees and using the rework station and nozzle. But, one of our manufactuirng location is not having the rework station. They rework it manually, using the hot air gun to remove the component. Then they place the new QFN component and solder the small portion visible on the side edges (as shown in side view in data sheet) using the soldering iron. But I believe, this will not allow much solder to flow below the part and form contact there as major portion of the pad is below the body of the QFN. Is this process reliable? Will it have any impact on the performance over a period of time? is there any other reliable manual process which can be used for this rework?
Appreciate all your help and response. Thanks in advance.
Rgds
Prashant

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