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

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Moisture sensitive components (MSC)

Juergen

#5278

Moisture sensitive components (MSC) | 20 February, 2001

Hi everyone

if once the exposure time is exceeded the only option is to bake the components. I learned there is an "old spec" for the baking conditions (24h/125C or 192h/40C) and a "new spec" which is the current standard specifying conditions of 48h/125C or 68days/40C.

My question: is there nothing between 40C and 125C? What about 60C or 80C? Sticks and reels do not stand a high temperature of 125C.

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#5289

Moisture sensitive components (MSC) | 20 February, 2001

To my knowledge, the 40C was established as the maximum "safe temperature" for all tape and reel packaging. The actual specs may vary somewhat for different types of reel, pocket-tape, cover-tape but you must be concerned with the cover tape adhesive also since higher temperature might affect the peel strength. Excessive warpage for sticks after the bake process is also a common issue.

I am not aware of any plans to include an intermediate temperature in the IPC/JEDEC standard. I am sure that the proper durations could be computed from the same mathematical models that were used for the existing tables, based on the sensitivity level and component body thickness.

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#5291

Moisture sensitive components (MSC) | 20 February, 2001

Time, time, time. There just never seems to be enough!!! Eh?

You�re correct. Depending on the material, some trays can take a high temperature bake, while other trays, in addition to tubes, and reels, require a low temperature bake. With this later group of carriers, long storage times at elevated temperatures can cause deformation of packaging, reduced solderability of components, and deterioration of the antistatic properties of the shipping carriers. The 40�C value you see quoted for low temperature baking is derived from properties of the material used to fabricate these carriers.

Get a copy of J-STD-033 [http://www.jedec.org/download]. It talks to bake times based on component thickness.

Consider these alternatives:

1 Use burn-in carriers.

2 Talk to your carrier supplier to determine the temperature their material can take. [The 40�C value maybe for wimps.] Bake at that temperature. To determine the temperature / time relationship: * Moisture permeability of materials is usually plotted linearly on log/log paper. * Weigh some dry components and compare that to some wet components.

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