Hello TechNetters--

I am interested to find out if anyone has had experience with bonded PCB
stiffeners.  More specifically, we are looking for some relative
physical and cost impacts to the option of bonding stiffening material
of some nature to the PCB to induce/control pre-assembly flatness
instead of installing a post-processing metal bar.

We understand that stiffening ability is going to be a function of
material and height but have not yet done any calculations on
alternatives.  In searching for some practical advice, we hope to direct
our efforts only at promising (if any) options.  The one caveat so far
is that in one case, the stiffener will need to be constrained to a max.
height of .187" for wave soldering clearance.  Other particulars of the
situation are as follows:

Size---------18"x12"x.090"
Material----FR-4 High Tg
Useage----Class 2 in a "glass house" enviroment

It is not yet known how large an issue this is going to be for us, but
considering the size of the cards, we understand the short- and
long-term problematic potential that this holds due to the component mix
of BGAs, Alloy 42 TSOPs, leadless r-networks, and press fit connectors.
Even though there will be an emphasis on copper balancing in every axis,
we don't expect that this will be the only solution needed.

Any feedback is welcome...

Gregg Peroutka
Adv Mfg Engr
StorageTek--Network Systems Group
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