PCB assembly bow and twist

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Dear Friends, I need your help to understand requirement... - Dec 26, 2013 by IgorFo

I expect to find the specification and measurement method fo... - Dec 27, 2013 by davef

IgorFo

#71529

PCB assembly bow and twist | 26 December, 2013

Dear Friends,

I need your help to understand requirements and measurement methods for bow and twist of assembled PCB (PCBA have and SMT and TH components). I already check all posts on the site but didn't found any related to my question answers. Our company produce PCBA for TV. Currently our customer began to claim us with problem of twisted boards. Our main concerns regarding this is next: IPC610 describe the requirements for SMT and TH PCBA bow and twist, which one we should use for mixed technology? and why it should be 0.75% IPC-TM-650 describe measurement for bare PCB and how we should measure bow and twist for PCBA. IPC-HDBK-001 says that we cannot use IPC-TM-650 for PCBA measurement at all. HOW we should measure bow and twist for PCB with SMT and THP components and what is the requirements for it

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davef

#71530

PCB assembly bow and twist | 27 December, 2013

I expect to find the specification and measurement method for the bow & twist of an assembly to be on the assembly drawing.

Comments are: * Expecting that an industry committee to write a bow & twist spec for an assembly they know nothing about is not well thought-out. * I've read tens of thousands of assembly drawings. I can not recall a single one with a bow& twist spec for the assembly. * If your bare board doesn't bows & twist, your assembly won't bow & twist, provided you don't really efff it up

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