Answering the question really requires reading between the lines.  IPC-610 doesn't allow for "excessive rework".  For us, that number is "something" less than 25% of the components.  An exact number depends on spacing, ease of rework, cost of the unit, even number of units affected.

IPC-TM-650 2.3.28 sets out guidelines for ionic surface contamination.  Heating the board draws out bromides from FR4, and rework usually means additional flux, either from cored solder or added straight.  For high mass components with close spacing, I could see allowing only minimal rework.  Then there's the risk of burning a board, lifting pads, etc.  The decision is more a question of economics.

Neil Flatter
TRW Automotive
Process Quality

>>> [log in to unmask] 10/02/03 12:00AM >>>
------------------------------
Date:    Wed, 1 Oct 2003 08:23:13 -0500
From:    Charles Caswell <[log in to unmask]>
Subject: Re: How many SMT capacitors / Resistors IPC Spec's allows to be        replaced?

All of the bad ones.

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