Doug,

You don't say whether the bend is a permanent, once only bend or a dynamic bend.

If it's a once only then that's dead easy for a mechanical engineer to calculate. Figure out where the
neutral axis is going to be (probably the outside of the coverlay on the inside of the bend) and from
there work out the strain on the copper. Then you have to figure out what the allowable strain is. For
rolled annealed (you'll have to ask the manufacturer) my unreliable memory tells me 10% is a
conservative figure.

If the flex is undergoing dynamic bending then the problem is one of fatigue. So in this case bend
radius (= stress) and number of cycles are both important. Generally it's regarded as a bad idea to
subject multilayer flexes to dynamic bending. For a single layer a rule of thumb is minimum bend radius
> 20 X thickness.

There are also a number of good design guides on the web whose addresses alas, I have also forgotten.
However you could start by looking for a flex manufacturer called Rogers I vaguely remember they had
some good stuff.

Hope this helps,



[log in to unmask] wrote:

> I am on project that requires that I determine the minimum bend radius of a
> flex circuit. I have not been able to find out any formulas or calculations
> to help out.
>
> I am a mechanical design engineer, so I am not up on all the terminology.
> It will of the class "Flex to Install", and will be of the adhesiveless
> type. Can anyone help out?
>
> Thanks.
>
> Doug
>
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--
Eric Christison
Mechanical Engineer
STMicroelectronics
33 Pinkhill
Edinburgh
EH12 7BF

Tel: (0)131 336 6165
Fax: (0)131 336 6001

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