We sometimes do bow and twist measurements on assembled boards, but only on small quantities (<10).
We place the PCBs on a granite table and measure the distance from the PCB to the table by focussing on various points with a lens with a small depth of field. Table and focus are motorised with X-Y-Z coordinates.
Takes quite a while because it's not automated. 


Best regards

Günter




> -----Ursprüngliche Nachricht-----
> Von: TechNet [mailto:[log in to unmask]] Im Auftrag von Giamis, Andy
> Gesendet: Mittwoch, 29. März 2017 06:01
> An: [log in to unmask]
> Betreff: Re: [TN] IPC-TM-650, 2.4.22, Bow & Twist
> 
> I have used precision blocks to create a picture frame and placed it on a
> precision flat stone.
> 
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Lum Wee Mei
> Sent: Tuesday, March 28, 2017 10:14 PM
> To: [log in to unmask]
> Subject: Re: [TN] IPC-TM-650, 2.4.22, Bow & Twist
> 
> It is this Bow & Twist season again.
> I often wonder whether someone really measured Bow & Twist on
> assembled boards. If yes, wonder how it was done as both sides are already
> populated with components.
> 
> ~wee mei~
> ________________________________________
> From: TechNet [[log in to unmask]] on behalf of Joyce Koo
> [[log in to unmask]]
> Sent: Wednesday, March 29, 2017 3:59 AM
> To: [log in to unmask]
> Subject: Re: [TN] IPC-TM-650, 2.4.22, Bow & Twist
> 
> it depends your design. if you have some small parts in the max bow area, it
> may flight out upon installation... (1) your PCB should compliant with bow
> and twist with simulated reflow - how many time you reflow, including
> rework if it required (2) your PCA depend upon what you how you want to
> install or support points and what is density and type of parts... better not be
> Gyro... those need really flat ;-).
> > Fellow TechNetters:
> >
> >    Does the above stated TM applies to raw cards ONLY?   Is there a
> > standard for PCBA?
> >
> > Victor,
> >