A couple of comments/observations:
* From our experimentation with the IPC-1951 resolution target, I conclude that anything up to 3 diopters is basically just a leveling of the playing field with respect to human nearsight acuity.
Unfortunately for us as specifiers, this isn't necessarily true at the 3-5 diopter breakpoint.  As I remember it, this basic assumption is the root of the PINs for the development of the IPC-1951.

* I believe we have the votes to install a minimum contrast/resolution for the magnification aid with respect to feature size.  The beauty of this solution is that we don't over-specify or under-specify, and allow the inspection activity to use the most efficient technique.

* There is an inherent problem with legibility requirements, in that a 3 day old baby has got better pattern recognition skills than any AOI.

* Increased magnification likely hinders pattern recognition, unless it increases contrast; which is usually not true.

I would be happy to submit a PIN to move to the next step with the 1951, but I think it might again fall under John's "critical and difficult" category.

Chris


-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Thomas E Kemp
Sent: Thursday, June 17, 2010 8:50 AM
To: [log in to unmask]
Subject: Re: [IPC-600-6012] Legibility of Marking

Let's put ourselves in the inspectors shoes for a moment. They are told to 
inspect a printed board visually, which includes marking in table 4-3, at 
3 diopters (1.75X) in paragraph 3.3. Then if they follow paragraph 3.3.5 
they are to refer to IPC-A-600 for legibility requirements, which states 
that they should inspect at no more than 2X. But IPC-A-600 also points to 
IPC 4781 which allows up to 3X. So, the inspector now has three different 
requirements for magnification tools to inspect marking, which puts it as 
a separate inspection from the standard visual. 

Now, how does the assembly operator read the marking? By the naked eye, by 
some magnification (I've seen 3X in use), or not at all (machine placed 
parts have eliminated much of the need for marking). Hopefully, the bare 
board inspection requirement will match the practical assembly need. And I 
agree with Joey, the markings have become ridiculously small and 
compacted.
Tom Kemp
Rockwell Collins Printed Circuits



Nick Koop <[log in to unmask]> 
Sent by: IPC-600-6012 <[log in to unmask]>
06/17/2010 01:47 AM
Please respond to
"(Combined Forum of D-33a and 7-31a Subcommittees)" <[log in to unmask]>


To
[log in to unmask]
cc

Subject
Re: [IPC-600-6012] Legibility of Marking






John,

I agree 2X seems more appropriate.  Higher magnifications are unlikely
to improve legibility, and the whole point of legend marking is to be
legible to the unaided eye anyway.

Nick

Nick Koop
Minco Products, Inc
Flex Circuits Product Marketing Manager
Ph 763 586-2846
Mobile 763 245-4825


>>> Thomas <[log in to unmask]> 6/16/2010 10:48 PM >>>
We indeed have an issue as 3.1.4 allows up to 3X! This needs to be 
addressed quickly. My position is 2X should be max.  Tom

Sent from my iPhone

On Jun 16, 2010, at 12:59 PM, "Dupriest, Don" <[log in to unmask]> 

wrote:

> Yea, looked at the 4781 some and it does good job of covering 
> "qualification testing" but I think I saw it points back to 6012 for 

> production lot testing.  So I think our job will be to add to table 

> 4-3 lot conformance AQL as required.  The table of qualification 
> test is too much so we just need to pick what makes good sense for a 

> lot to lot check.
>
> C. D. (Don) Dupriest
> Lockheed Martin - MFC
> Advanced Manufacturing Technology
> member of:
> Production Technical Excellence Staff
> Ph. 972/603-7724 fax: 972/603-9052
> Email: [log in to unmask] 
>
>
>
>
> -----Original Message-----
> From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of John 
> Perry
> Sent: Wednesday, June 16, 2010 2:45 PM
> To: [log in to unmask] 
> Subject: Re: [IPC-600-6012] Legibility of Marking
>
> Hi Wendi and Don,
>
> When we revised IPC-A-600 and IPC-6012, we put pointers in both of 
> those documents to the new IPC-4781 qualification and performance 
> specification for legend and marking inks (released in 2008).  Prior 

> to IPC-4781, there was no industry standard for legend and marking 
> inks aside from an obsolete MIL spec.
>
> This document is modeled after IPC-SM-840 for solder mask, and like 

> that document, has requirements for adhesion to printed board 
> laminate as well as solder mask.
>
> We say in 3.2.10 of IPC-6012C that "Marking inks shall be permanent 

> and shall conform to IPC-4781 or be as specified in the procurement 

> documentation.
>
> I agree with Don though, that we should examine this further within 

> our two task groups.  IPC-A-600H says the boards shall be inspected 

> at no greater magnification than 2X for marking legibility. 
> IPC-4781 says the following:
>
> 3.1.4 Legibility After marking is tested in accordance with the 
> methods outlined in this document, excluding flammability, markings 

> which are missing in whole or in part, faded, smeared, or shifted 
> (dislodged) to the extent that they cannot be readily identified at 

> not more than 3X
> magnification, shall constitute failure.
>
> Opps...
>
> Best Regards,
>
> John Perry
> Technical Project Manager
> IPC ? Association Connecting Electronics Industries(r)
> 3000 Lakeside Drive # 309S
> Bannockburn, IL 60015-1249 USA
> +1 847-597-2818 (tel)
> +1 847-615-7105 (fax)
> +1 847-615-7100 (Main)
> [log in to unmask] 
> www.ipc.org 
>
>
>
> -----Original Message-----
> From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of 
> Dupriest, Don
> Sent: Wednesday, June 16, 2010 1:55 PM
> To: Listserv IPC-600-6012
> Subject: Re: [IPC-600-6012] Legibility of Marking
>
> Hi Wendi, I would say yes it applies to component marking (reference 

> designators).  Examples in 600 mostly reflect numbering (like 
> traceability) but one example photo shows a component symbol.  As to 

> legibility; I would prescribe to if you can interpret the letters or 

> symbol with 2X it is fine.  However, this section probably could 
> stand some more work.  One thing we have noticed is 6012 does not 
> specifically address adhesion for marking like solder mask is 
> covered in 600 and 6012.  It references a permanency requirement so 

> one would assume tape test and/or solvent resistance would be 
> applicable.  But a tape test may be too difficult to pass for some 
> really small feature sizes/designator letters.
>
> Guess just another thing to add to the committee to do list.
>
> C. D. (Don) Dupriest
> Lockheed Martin - MFC
> Advanced Manufacturing Technology
> member of:
> Production Technical Excellence Staff
> Ph. 972/603-7724 fax: 972/603-9052
> Email: [log in to unmask] 
>
>
>
> -----Original Message-----
> From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Wendi 

> Boger
> Sent: Wednesday, June 16, 2010 1:05 PM
> To: [log in to unmask] 
> Subject: [IPC-600-6012] Legibility of Marking
>
> Everyone,
>
>
>
>    Does section 2.8 Marking in IPC-A-600 apply to Legend (component
> mark)?    We are increasingly seeing designs with very small legend
> features causing discussions at final inspection as to whether they 

> meet
> the requirement for legibility.  From what I understand legible 
> means at
> no more than 2x you can understand what the symbols are.  Fussiness 

> and
> filled in holes in letters are allowed if you can tell what the
letter
> is.
>
>
>
>    Would appreciate some guidance on this.
>
>
>
> Thanks,
>
> Wendi
>
>
>
>
>
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