Mr. Franck,
Procedure 1 (Figure 1) is for bow (only) and is determined by measuring the maximum
deflection with all 4 corners in the same plane (touching a surface plate). Allowable bow is a
percentage of the length of the side exhibiting the maximum deflection.
Procedure 2 (Figure 2) is for twist (only). The board has twist when you can't get all four
corners to touch the flat surface plate. Allowable twist is a percentage of the diagonal
measurement.
The two procedures are used for measuring two different characteristics, bow or twist. You are
not given a choice of the two procedures for measuring bow.
>From IPC-A-600D, pg 51, Table 10-3 "Bow and Twist Tolerances for Glass Base Material"
For Multilayers, All Thickness categories: Class I = 2%, Class 2 = 1.5%, and Class 3 = 1%.
On Wed, 31 Jan 1996 08:21:22 -0500 George Franck X2648 N408 wrote:
> From: George Franck X2648 N408 <[log in to unmask]>
> Date: Wed, 31 Jan 1996 08:21:22 -0500
> Subject: Bow and Twist
> To: [log in to unmask]
>
> IPC-TM-650 2.4.22 is the test procedure for bow and twist. It is found in
> various documents, mine is in the back of my trusty IPC-RB-276. In section
> 5.4 Procedure 4, Production Testing using a "go/no-go" pin gague, there are
> two methods and measurements. The first, in para. 5.4.1, (fig 6) show the
> bowed board place cup side down and the measurement is the gap under the
> cup. In 5.4.2, (fig 7) the board is turned over and the cup is up. The
> measurement is at the edge or corner of the board.
>
> My question is this. The cup side up measurement is about twice the cup
> side down measurement. Must both measurements meet the percent deviation
> requirement? Is there a different way of calculating the maximum
> percentage deviation for the two? I am confused.
>
> You can see what I am talking about by taking out a business card, and
> curling it a little. Now put it cup side down, look at the gap. Turn it
> over and hold down two corners (across the edge which does not have the
> curl in it), the gap is about twice as much.
>
> Thanks and don't let your boss catch you playing with your cards at your desk!
>
>
>
====================================================================
> George Franck
> PWB Product Assurance Phone (703) 560-5000 x2648
> E-Systems M/S N408 Fax (703) 280-4613
> 7700 Arlington Blvd E-Mail: [log in to unmask]
> Falls Church Va 22046 E-Mail: [log in to unmask]
>
====================================================================
>
>
FRED J. PAUL FLUKE CORPORATION
Sr. Process Engineer POB 9090 M/S 55
PCB Operations EVERETT, WA 98206
[log in to unmask] 206 347-6100
voice: 206 356-5734 (w Voice Mail)
fax: 206 356-6070
[Ideas and expressions presented herein are my own, and in no way are they implied to
necessarily represent those of the FLUKE CORPORATION]
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