Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Thermal Conditions Causing damage to MSDs

Yves Trudell


Thermal Conditions Causing damage to MSDs | 12 January, 1998

In general terms, guidelines for moisture sensitive devices (MSDs) say that you shouldn't put a component through reflow after it has reached its exposure limit with respect to moisture absorption. When using an automated hot air rework tool to remove and replace an SMT component, there is a risk of damaging the neighboring components if they have absorbed enough moisture and if they get enough heat. For this reason, heat shielding is used for protection and assemblies are baked prior to repair. Assuming that a component has surpassed its exposure limit and has enough moisture content to be damaged when put through a reflow cycle, what minimum conditions (max. temp., ramp) would be required to cause moisture damage (i.e. delamination or popcorning)? If neighboring components are thermally profiled during the rework cycle and it is shown that they do not receive enough heat to cause moisture damage, product baking and heat shielding may not be required. Any ideas? Yves Trudell Quality System Engineering Nortel, Wireless Networks Calgary

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