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SMD flatness standard

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SMD flatness standard | 17 November, 2006

Good afternoon all,

There is an issue in my company regarding flatness on SMDs. The part I am fabricating is a multilayer assembly of .175" by .175" by .049" thick. The part is made out of a multilayer copper clad PTFE with a tin finish surface.

After dicing the parts (boards), there is a slight stretch of the PTFE (material lift or semi burr) that is about .002" or less. It is not a metal lift as there is no separation of neither the tin to the copper or the copper to the PTFE.

Is there any standard talking about flatness requirements on SMDs?

Tahnk you, Fernando

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SMD flatness standard | 18 November, 2006

Bow & twist: IPC-A-600. Acceptability of Printed Boards 1.5%; Goal 0.005" per inch; Practicle 0.007" per inch

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SMD flatness standard | 18 November, 2006


May I ask where did you find the 1.5%, or the goal of .005" (or .007") per inch?

The IPC-A-600 bow and twist standard calls for a .75% based on the calculation of the test method TM-650, method 2.4.22, which calculates the percentage based on the length and/or width of the piece with a given maximum bow allowed, or a maximum allowable twist. Both of these parameters are unknown to me.

As far as I remember, the IPC-A-600 does not mention any goal of either .005" or .007" per inch. Please let me know whether there is a revision of the IPC-A-600 that would mention such a goal as the one I own, RevF., does not seem to have it, at least from what I remember at this moment.

I really appreciate your help. I would really love to see a standard giving something along the lines of: SMDs should be completely flat with a tolerance of +.005" -0.00"

Thank you again, Fernando

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SMD flatness standard | 19 November, 2006

When you say "SMD" I am assuming you are refering to a component. But in your description you mention these are some type of "boards".

"flatness" or coplanarity is a function of the application and process.

I think in your case your standards would fit under form-fit-function. The application and process will dictate your final flatness specification.

Example: I have a customer who's product requires a flatness spec. of "no greter than 0.005in. from planar". Hmmm. That's odd. But then you look at the final assembly and see why they need this board kept flat.

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SMD flatness standard | 20 November, 2006

Good morning Ken,

Thank you for your feedback. Just as a clarification, SMD stands for Surface Mount Device. Although my end product, in this case, is a SMD, it might be also referenced as a board.

In the other hand, what I get from your feedback is that the application (customer) will be the one dictating the flatness requirement, and that there is no standard calling out a requirement of this type.

Thank you again for your feedback, Fernando

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SMD flatness standard | 20 November, 2006

Sorry for stating this incorrectly. It should been: Bow & twist for bare boards and panels: IPC-A-610 Acceptability of Electronic Assemblies, 10.6: 1.5% for PTH only and 0.75% for SMT, acording to test method TM-650, method 2.4.22

IPC-6012, par. 3.4.4 Surface Mount Product: 0.75% of PCB diagonal measurement = 0.0075 inch / inch All Other Product: 1.5% of PCB diagonal measurement = 0.015 inch / inch

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