heavy mechanical shock problem in my board!!

Hi friends
I have a project with heavy mechanical shock, my board has a microcontroller, acc meter sensor, crystal, v-regulator and some resistor and caps. my problem is heavy mechanical shock that is about 5000 G!
heavy acc cause by explosion that is for throwing my board, it will damage board and some parts, i need some help to find a way to care about main board and components and i want to understand how much is parts resistance against mechanical shock ( i know my acc meter can resist 8000G but not other electronic components ), and i want to find somthing like silicone glue to protect main board against first heavy shock. I have used resin and mazda silicone glue but those are not good!
or should i use special kind of electronic board??!!
+ i have onlly one time shock not long time, it's throwing shock!
Regards

Encapsulate the whole board in epoxy resin?
Frank

chuckey said:

Encapsulate the whole board in epoxy resin?
Frank

Click to expand...

yes, resin has broked!

There are places you want rigidity (to prevent movement), however this is also associated with brittleness. Therefore there are places you want flexibility (to allow tiny movement).

It would help if you could arrange for the board to accelerate and decelerate more slowly. Can you mount the board so it has some flexibility? On cushioned standoffs? Anchor its corners in sponge rubber? Encase it in a foam enclosure? (Watch for static charge.)

Lightweight and miniaturized components are good. (This probably means surface mount where possible.) All components should be snug to the board. A lightweight component can be soldered by its leads to the board.

A heavier component could pull its leads out of the board. It should be tied to the board.

The crystal. I do not think it should not be rigidly mounted to the board. It has a mechanical element. Shock could ruin it. I picture that it should be mounted it on a foam standoff, 1/16 or 1/8 inch high. Use non-metallic line wrapped around it, and tie it to the board. Make the leads very thin, and slightly flexible if you can, so they do not transfer sudden acceleration to the crystal element.

How to test a board for shock? A paint mixer applies continuous shaking. A cheaper method is to bang its edge with a hammer. I have no idea what G-force this is equivalent to.

Hi,

Encapsulate the whole board in epoxy resin?

Click to expand...

Did you consider to use a soft potting material?

Elastic materials like cured silicone or rubber may generate resonant frequencies. Therfore I tend to shock absorbing (mechanical power absorbing = damping) material like silicon gel.

Maybe worth some tests..

But 5000G is huge. I don´t want to feel it. ;-)



Klaus

BradtheRad said:

The crystal. I do not think it should not be rigidly mounted to the board. It has a mechanical element. Shock could ruin it. I picture that it should be mounted it on a foam standoff, 1/16 or 1/8 inch high. Use non-metallic line wrapped around it, and tie it to the board. Make the leads very thin, and slightly flexible if you can, so they do not transfer sudden acceleration to the crystal element.

How to test a board for shock? A paint mixer applies continuous shaking. A cheaper method is to bang its edge with a hammer. I have no idea what G-force this is equivalent to.

Click to expand...

I have changed crystal with rc osc and it's ok. the board is smd and main problem is with acc meter chip that is in QFN package.
I have 8 board for test in real condition, i had 4 test untill now, 2 of them with epoxy resin and 2others with silicon glue, in first test resin broked and caused board damage, in glue version board was ok but QFN chip and smd capacitore faile! maybe foam is better!!
it's 2 side smd board.
Here we don't have continues shock, it's only one sock of explosion to throw and it's about 5000 G! just primary shock that is so big!
thanks for your answer

It sounds like the larger components are breaking because of PCB board flexing on impact. Possibly solder on board stiffeners in the problem area and give the board a controlled place to flex.