Steve,

Sorry about the delayed response, but I've been on the road again this
week. With a 2" bend radius the copper will only experience 0.035% max
strain. Since this is well within the elastic range for the foil 30M
cycles should be no problem. Having said that, I don't have any data on
what I assume is silver epoxy. The max. strain in those layers is 0.14%
but I don't have the information to be able to translate that into flex
performance.

Many other considerations can also effect flex life:

Surface finish, edge straightness, and side-wall profile of the traces
can create stress concentrations if nonuniform.
Foreign material trapped under the coverfilm can create local stress
concentrations, and may unbalance the circuit.
Improper selection of adhesive thickness, excessive squeeze-out, or
mixing of adhesive types can unbalance the circuit.
Poor coverfilm bond can lead to delamination, and rapid destruction of
the circuit in testing.
Nicks or cuts in the polyimide along the edges of the part can act as
tear propagation sites.
Handling damage can wrinkle the copper and cause early failure.
Wrinkles or creases in the polyimide, formed during lamination or
application of a stiffener, can affect the free movement of the flex.
This distorted geometry can lead to high impulse loads during cycling.
Solder on the copper in the flex area can unbalance the circuit.

If you have the physical properties of the silver layer you can analyze
your design with my flex analysis software located at:
http://www.geocities.com/CapeCanaveral/Launchpad/9641/program/program.html

Andy Magee
Flex Guru - Consulting
[log in to unmask]
(937) 435-3629


Steve wrote,

Does anyone know if the following construction will handle 30,000,000
cycles with a 2 inch bend radius.
.0005 Kapton
.001  Adhesive
.0006 Silver
.0005 Kapton
.001  Adhesive
.0014 RA COPPER
.001 Adhesive
.0005 Kapton
.0006 Silver
.001  Adhesive
.0005 Kapton

Total  .0086

Some copper tracks will be .150 wide with .010 signal tracks in between
- I also have to individually shield the
copper tracks with the silver.

Thanks Steve Kelly - [log in to unmask]

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