Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Board Stress

Mike Cox

#12882

Board Stress | 19 January, 1999

I need some opinions (And I know everybody has one). I am mounting a board into a case, after mounting the board I am loading it with stress in the middle causing it to bend around .030 inch. The board is 4" X 6" and is Bending in the 4" direction. The board is gold flash and is used for consumer electronics (Sub aquatic sonar, biologic locating device) What is the possibility of getting latent failures from joint stress? Are there any specs that address this issue? I think I need a drink Mike

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Earl Moon

#12883

Re: Board Stress | 20 January, 1999

| I need some opinions (And I know everybody has one). | I am mounting a board into a case, after mounting the board | I am loading it with stress in the middle causing it to bend around .030 inch. The board is 4" X 6" and is Bending in the 4" direction. The board is gold flash and is used for consumer electronics (Sub aquatic sonar, biologic locating device) What is the possibility of getting latent failures from joint stress? Are there any specs that address this issue? I think I need a drink | Mike | Drink hearty Mike as you might be running a meaningful experiment for us all. If you could have placed and soldered the components in the bent position, you might prolong solder joint reliability. Depending on mechanical and thermal factors as device type (wheter compliant leaded or not),stress, and shock, you might succeed, but does anyone really know?

My other concern might be for the PCB. It may suffer significantly over time even though .030" seems a small amount of wrap around the old pole, rigid boards are neither designed to flex for install or operation.

Should be interesting,

Earl Moon

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Dave F

#12884

Re: Board Stress | 20 January, 1999

| I need some opinions (And I know everybody has one). | I am mounting a board into a case, after mounting the board | I am loading it with stress in the middle causing it to bend around .030 inch. The board is 4" X 6" and is Bending in the 4" direction. The board is gold flash and is used for consumer electronics (Sub aquatic sonar, biologic locating device) What is the possibility of getting latent failures from joint stress? Are there any specs that address this issue? I think I need a drink | Mike | | Mike: I'll give you a half (two thirds) hearted support. Your boards are 0.75% out-of flat (100*0.03/4.00), if I haven't messed-up the math. Opinion #1: I think your boards should be accepted best two out-of three:

1 IPC-A-600 allows bow & twist of 1.5% 2 Rule of thumb (Opinion #2) #1: Goal 0.005" per inch; practicle 0.007" per inch. See I'm usin' opinions to support my opinions. Now that's delux opinionation. None the less, you don't make on this count, bud. 3 Rule of thumb (Opinion #3) #2: IPC-A-600 1.5% for PTH only and 0.75% for SMT

... but next time I'm out in my bass boat with my Poppel Pocket Fisherman, and a delicate piece of electronic gear, and I'm not reelin' those puppies in, I'ma gonna pop the cover off that dude and check for warped boards and a faint wiff of an adult beverage.

TTYL Dave F

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