My first attempt at flex circuits

[SCSKITS]

Recently had the opportunity to do a couple of (similar) flex circuits for some Tektronix gear that my son was repairing. The original TEK part numbers are 259-0193-00 and 259-0155-00 and -01. They are pretty simple, a switch pattern and two LEDs, one green and one red. The originals had a single package with the LEDs, I opted for some 0603 LEDs.

I was able to get dimensions from the original parts and then compared a 1 to 1 print to the original. Fortunately, the switch contacts were the intermittent connection, so it was easy to determine the LED color and orientation using a multi-meter in diode mode.

The main thing I had to research a bit was the backing at the contact end and under the switch contacts. JLCPCB had some on-line help that made it easy. I just created a mechanical layer for the outlines and filled in data for material and thickness on their site.

The 259-0155 part is slightly different from the -00 to the -01 so I added a small jumper to connect the contacts that are connected on the -01 version.

The 259-0193-00 is installed and functional. Still waiting to hear on the 259-0155-01, it just arrived yesterday, so may be a few more days. I do not expect any issues since the first one worked OK.

What do you think???

[PlainName]

Nice, but the corners should be radiused to remove stress point. Particularly, the acute angle will tend to cause tearing. The tracks would benefit from being curves too (just follow the smoothed perimeter). There are other tracking issues, most of which are covered here:

https://resources.altium.com/p/bend-reliability-trace-geometry-materials-flex-lifespan

[SCSKITS]

Thanks for the feedback including the link, it will be useful if I do another..

These were done to match the TEK parts, maybe too exact based on your comments.
It looks like a lot has been learned since the originals were made.

At least these only have to bend one time then they are set in place.

ed

[Randy222]

Are the darker sections thicker/layered?

[SCSKITS]

Yes, they have a stiffener added to the back side

[Doctorandus_P]

For a small amount of bending cycles, a flex PCB like this is just fine. The small details that remove all stress concentrations (such as sharp corners in tracks or outline and holes) are only important when many bending cycles are expected.

[twospoons]

There's also the minimum bend radius to take into account. This will get larger for thicker flex and for multilayer flex.  Its possible to break tracks with a single bend that's too tight, especially for tracks on the outside of the bend.  Your flex manufacturer should be able to advise minimum bend radius.