Yep. You've referenced the 6012 bare board as-fabricated requirements that are reprinted in A-610 with the weasel word "should" attached to post assembly.
6012D added good detail regarding how to handle pallets (at completed bare board level). And if you parse the 6012 verbiage carefully, it says that method 2.4.22 is only attached to the *calculation* of percentage of "bow" and "twist".
We call this the "IPC flatness model" as opposed to the common ANSI model.
So, IMO the answer to Victor's question is: measure your assembly using whatever contact/non-contact method you think is suitable, just make sure that you use the IPC model for bow and twist.
If it those percentages exceed 1.5/0.75 PTH/SMT, you need to go look at your bare boards. If they conform, you're stuck with "should" at assembly level. If they don't conform, you may still be stuck with AABUS due to "unbalanced" caveat.
And of course, the unbalanced caveat is the real meat here, because it is what causes the problem during soldering (other variables held equal) and points blame towards design activity.
Chris
-----Original Message-----
From: Stadem, Richard D [mailto:[log in to unmask]]
Sent: Tuesday, May 22, 2018 9:01 AM
To: TechNet E-Mail Forum <[log in to unmask]>; Chris Mahanna <[log in to unmask]>
Subject: RE: [TN] Bow and Twist measurements per IPC 650 TM 2.4.22, IPC 600-2.11 Flatness
Au contraire.
Bow and twist requirements must be met during or after assembly per IPC-A-610 as per figure 10-23, on page 10-13, to be less than 1.5% for PTH, and less than .75% for SMT. IPC-610 also refers you to IPC-TM-650 method 2.4.22, as does the J-STD-001, IPC 6012, and as a condition for fabricated circuit boards, IPC-A-600. They ALL refer you to method 2.4.22, and they ALL have requirements for maximum bow and twist throughout all stages of fabrication and assembly.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: Monday, May 21, 2018 4:24 PM
To: [log in to unmask]
Subject: Re: [TN] Bow and Twist measurements per IPC 650 TM 2.4.22, IPC 600-2.11 Flatness
To my knowledge, there is no IPC standard requirement (or method) for during/post assembly; much to the package manufacturer's chagrin.
Chris
Chris Mahanna
Robisan Laboratory Inc.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of [log in to unmask]
Sent: Wednesday, May 16, 2018 11:04 AM
To: [log in to unmask]
Subject: Re: [TN] Bow and Twist measurements per IPC 650 TM 2.4.22, IPC 600-2.11 Flatness
Folks,
Is there a consensus, especially from committee (7-11D) members, on the above inquiry regarding Bow & Twist for raw board and PCBAs (populated boards)?
Ref: IPC-T-50M (May – 2015) ( Victor’s comments )
Bow - (Fabric) Filing yarn that lies in an arc across the width of a fabric.
Twist - The deformation of a rectangular sheet, panel, or printed board, that occur parallel to a diagonal across its surface, such that one of the corners of the sheet is not in the plane
that contains the other three corners.
Victor,
From: Jose A Rios [mailto:[log in to unmask]]
Sent: Wednesday, May 16, 2018 8:35 AM
To: TechNet E-Mail Forum; Hernandez, Victor G
Subject: Re: [TN] Bow and Twist measurements per IPC 650 TM 2.4.22, IPC 600-2.11 Flatness
2.4.22 is only for bare (unpopulated) PWB’s, and the rigid portion of rigid-flex PWB's. Section 1 (Scope) explicitly excludes PCBA’s from being evaluated using this method.
José (Joey) Ríos, Sr QA Engineer
Mission Assurance Manager
Kavli Institute for Astrophysics & Space Research Massachusetts Institute of Technology [log in to unmask]<mailto:[log in to unmask]>
(617)324-6272
On May 16, 2018, at 7:17 AM, [log in to unmask]<mailto:[log in to unmask]> wrote:
Fellow TechNetters:
Is there a separate Bow & Twist Test/documentation for Printed Wire Boards, PWB, and Printed Wire Board Assemblies, PWBAs? Are they interchangeable......
Victor,
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