Hi Victor:
I know this is a little late for an answer but this is what I found out.
When the twisted board had three corners touching three same level posts the difference between that height and the fourth corner was 42 thousands or 42 mils or 0.042".
by 5.2.7 0.14% was obtained With ***** 42 mils ******
by 5.3.6 referee method R1 - R2 was **** 36.5 mils ***** The second number is too close to the first one to be true. The number should have been about 16 mils.
Using the referee method two opposite corners should be touching two same level posts or be at the same datum. The other two corners should also be at a same different datum. Viewed from the proper perspective the board should be like a V. The difference of the top corners from the bottom corners divided by length times 100 should give 0.14%.
Perhaps you do not have the board any more, my conclusion is that R1 and R2 reading that you obtained are not correct.
Regards,
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Victor G. Hernandez
Sent: Tuesday, September 28, 2004 3:43 PM
To: [log in to unmask]
Subject: [TN] PCB Raw card Bow & Twist calculation Ref: IPC-TM-650
Fellow TechNetters,
Anyone out there cares to put in their 2¢ worth. I sure would appreciate the CLARIFICATION.
Given the following physical dimensions of a raw card I proceeded to apply the IPC-TM-650 Bow and Twist Method 2.4.22 step 5.2.2 for maximum allowable twist percentage for an SMT, ,75%, technology card. Then confirmed that calculated thickness by applying 5.2.7 formula to confirm the SMT tolerance, .75%, guideline. I also conducted the 5.3 Referee method (Twist) for a second correlation. The 2 methods do not yield similar data. Can you please help to explain where I went wrong.
Sample #1. Length: 1.5 inches,
Width: 10.4 inches,
Diagonal: 14.75 inches,
Thickness: 0.062 thousands.
Technology: SMT
Target: 0.75%
5.2.2 Maximum Allowable Twist R = 2(D)(T)/100 = 2(14.74)(.75)/100 = 0.22125
5.2.7 Percentage Twist R = R/2(D)x100 = .22125/29.5x100 = .75
Therefore, the max allowable twist Go/No-GO thickness is 0.221125
I proceeded with the exercise.
I place the sample on a granite rock. While penning one edge of the sample I slide a Go/No-Go thickness gage on the corner onsite the pin edge which measured .042 thousands. Now applying the formula for actual percentage twist.
R = R/2(D)x100 = .042/29.5x100 = 0.14237
The value of .14% is well below the maximum allowable .75% percent twist, acceptable product.
I proceeded with the exercise:
5.3 Referee Method.
Actual: R1 = 0.0955
R2 = 0.0590
5.3.6 Percentage Twist = R1-R2/Lx100 = 0.0955 - 0.0590/10.5 = 0.0034761 = .34%
The results of 5.2.7 actual does not correlate to the results of 5.3.6. What's missing.
In advance I thank you for your timely response in this matter.
Victor,
-----Original Message-----
From: Guy Ramsey [mailto:[log in to unmask]]
Sent: Tuesday, April 20, 2004 4:16 PM
To: 'TechNet E-Mail Forum.'; Hernandez, Victor G
Subject: RE: [TN] PCB Raw card Bow & Twist Tolerance
For bow it is the length of the board. For twist it is the diagonal. But these are not "requirements" they are "should" best manufacturing practices. Bow and Twist shall not be sufficient to damage the components or solder connections in subsequent assembly operations.
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor G.
> Hernandez
> Sent: Tuesday, April 20, 2004 5:00 PM
> To: [log in to unmask]
> Subject: Re: [TN] PCB Raw card Boe & Twist Tolerance
>
> Ramon,
>
> I have seen the 1.5% and 0.75% criteria before. What I
> am not sure
> is % of what base number.
>
> Victor,
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
> Sent: Tuesday, April 20, 2004 1:07 PM
> To: [log in to unmask]
> Subject: Re: [TN] PCB Raw card Boe & Twist Tolerance
>
>
> Hi Victor:
> It should definitely be less than 1.5% for THT and
> less than 0.75% for SMT, which that is what it is for a board after it
> has been soldered.
> JStd.001B 9.2.3
> Regards,
> Ramon
>
> > -----Original Message-----
> > From: Victor G. Hernandez [SMTP:[log in to unmask]]
> > Sent: Tuesday, April 20, 2004 1:02 PM
> > To: [log in to unmask]
> > Subject: [TN] PCB Raw card Boe & Twist Tolerance
> >
> > Steve,
> >
> > What has been your experience with measuring Bow &
> Twist on a raw
> > card. Is there a RULE Of Thumb that can apply generically.
> >
> > Victor,
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