Juanita,
Good question. This is an issue that is often overlooked during
facility planning. As it happens, I have dealt with that same question
over the last year. My points of concern have been:
* Dendritic growth, electrolytic corrosion, and solderability problems
are all accelerated by higher humidity levels. This is of particular
concern if you perform environmental testing or any other operations
that expose your boards to high temperature under power. Coming from S.
Florida I can attest to the effects of humidity on your PCB's. So for
this reason you want to keep the humidity levels in your plant down. I
like to see under 50% RH.
* Potential for ESD damage is inversly proportional to the level of
humidity present. Given that, it is an obvious advantage from the ESD
viewpoint to keep humidity levels greater than 50% RH. I saw the ESD
problems in California's dry air and consider that a serious concern as
well..
So depending on your exposure to these two opposing concerns you may
want to shift above or below the 50% mark. Someone on the net may be
able direct you to a substantive study but my experience suggest
assuring your air system can maintain a 30-70% range and then
controlling the range according to your particular case.
I believe workers would be reasonably comfortable anywhere in the
mentioned range so that issue should take care of itself.
good luck.
Steve tucker, Mfg. Eng., AlliedSignal Aerospace
>----------
>From: Juanita Zeinstra[SMTP:[log in to unmask]]
>Sent: Friday, January 16, 1998 12:30 PM
>To: [log in to unmask]
>Subject: [TN] Assembly Floor Humidity Requirements
>
> We are located in Grand Rapids Michigan. We are moving across town to
> a new building which is being renovated to suit our needs. With a
> tight budget getting tighter, there is a somewhat political and
> emotional contest in the making.
>
> By title our assembly facility will be called the "Engineering
> Manufacturing Development Center (EMDC)". Engineering activity is
> located in Grand Rapids, Mi. while production manufacturing will be
> located in Clearwater, Fla. The EMDC will have process development,
> low volume and transition responsibilities.
>
> We assemble primarily SMT boards but there is some thru-hole and mixed
> technology as well. Processing in the EMDC includes wave, vapor
> phase, and hand soldering. IR, convection ovens or even new technolgy
> soldering may be added later, as well. Our boards are primarily rigid
> polyimide boards but flex and rigid-flex boards are processed
> occasionally. Thermount boards are being considered for the future.
> Cu-Invar-Cu and Cu-Mo-Cu stabilizing cores are frequently employed for
> CTE stabilization.
>
> We will be using more and more plastic and commercial parts and less
> of the ceramic and military grade parts, as is the industry trend. It
> also goes without saying that expect to track industry trends in
> technology, components and processing.
>
> We are in the business for the long term. We started our operations
> in GR in the early 1950's and we will have a 20 year lease on our new
> facility. Our business niche is high technology commercial and
> military avionics. Our facility size is almost 900,000 Sq.Ft. and the
> EMDC and circuit card assembly areas could be as large as 15K-25K Sq.
> Ft. in size.
>
> With that as background, the question is as follows;
>
> What temperature / humidity requirements would you recommend for
> the EMDC and assembly areas of our new facility?
>
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