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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Bow and twist of PCB's

Dougie

#6026

Bow and twist of PCB's | 20 April, 2001

Hi,

I've just splashed out �60 on IPC-A-600F trying to find out the formula for measuring the bow and twist of raw PCB's. Much to my dismay there are 10 lines on the subject in the whole standard. Worse still is that it tells me nothing I don't already know. Topping that off, it refers me to IPC-TM-650 where I can find the method of measurement. This all comes at a price though, another �240!!!

Does anybody know the formulas from the 650 standard?

Its all about board dimensions, length across diagonals and heights raised etc, but I don't quite know the order to put them in!

Go on, save me �240 it is Friday after all! Just imagine that warm smiley feeling you'll have knowing that you've helped a fellow engineer in his hour of need.

Cheers, Dougie.

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#6027

Bow and twist of PCB's | 20 April, 2001

Dougie,

oh yes, it�s a bit short that chapter. I have the Revision e in front of me and this one contains in the appendix the needed IPC-TM-650 Test method for bow and twist.

Can�t think that they don�t have that in the new revision.

Hope you find that chapter

Wolfgang

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#6028

Bow and twist of PCB's | 20 April, 2001

In short:

the measured deviation / the length this deviation occurs * 100% = % of deviation

Actually we encounter mostly "twist" so we put the board on a flat surface, hold it down at the corners to see if any of the corners lifts, measure the height if somethings comes up, divide by the diagonal of the PCB, multiply by 100 and get the percentage we need to reject or accept the board.

We accept 1%.

Wolfgang

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Kris W

#6036

Bow and twist of PCB's | 20 April, 2001

Hey Dougie,

If you go to IPC.ORG and click on the on-line resources and databases, then on the "free downloads" link, the second or third document "for free" is the IPC-TM-650 in its entirety.

It does discuss the test you are looking for!

Have fun!

Kris

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Dougie

#6043

Bow and twist of PCB's | 23 April, 2001

Hi Kris,

DISCO!!!!

Cheers, Dougie.

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CAL

#6048

Bow and twist of PCB's | 23 April, 2001

650 Standards are also located in the back of IPC JSTD-001. I am currently looking at 4 pages on bow and twist. Percent bow = R1-R2/L x 100 (R1= Highest point; R2=lowest or resting point; l= length) Percent twist=(R1-R2)/(2xL)x 100

Sorry if this is not clear Cal

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Ryan

#6053

Bow and twist of PCB's | 23 April, 2001

Dougie-

We,too, have the IPC-A-600F, and the spec. refers to IPC-TM-650 test method in the back of the book. Look on page Number 2.4.22 of the test methods appendix. This outlines the procedure for determining the percentage of bow and twist, the limits of which are set forth in 2.11 of the standards section.

-Ryan

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CAL

#6054

Bow and twist of PCB's | 23 April, 2001

Ah Yes.............My 600 A version has it in the back as well

Cal

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