See, I agree.

> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Kathy Kuhlow
> Sent: Tuesday, December 30, 2003 2:51 PM
> To: [log in to unmask]
> Subject: Re: [TN] IPC Board Quality
>
>
> Oh well, but the question was would you expect a class 3 in
> the assembly.  I wouldn't expect anything I had not made
> known in some method of communication.  As someone living in
> the contract world I wouldn't take anything for granted.  If
> I went back to the OEM world I would ask for a class 2 PCB
> and a class 3 assembly based on some of the exact class
> requirement differences you mention.  I have a hard time
> accepting the class 2 minimum solder joint especially through
> hole with blow holes and voids as only being process
> indicators.  I know of a few OEM's that have been burned by
> the minimum class 2 solder joint for industrial products.  To
> remedy this they put a little more money into the product and
> ask for a class 3 assembly but leave the PCB at a class 2.
> Class 2 is what they really want but to make sure they don't
> hit that bottom line of minimal they ask for a class 3.  I
> think there are more class 3 products being built only
> because of the class specifications not the end use of the product.
>
> Kat
>
> >>> [log in to unmask] 12/30/03 01:13PM >>>
> Very rarely do I disagree with Kathy. But, this time I think
> I do, perhaps, a little.
>
> Yes, you can get Class 3 solder results from boards that were
> fabricated under contract to Class 2 requirements. But, at
> least one variation allowed by IPC-A-600 and IPC-6012A for
> class 2 can result in material conditions that may not yield
> Class 3 results at the assembly level.
>
> Plating voids in PTH are not allowed for Class 3 but a
> limited number are allowed in Class 2 products. Plating voids
> can produce blow holes in solder joints. These are process
> indicators for Class 2&3. We have, however, observed blow
> holes that exceeded the 30 degrees circumferential fillet
> variation allowed for Class 3. The product would have passed
> Class 2 acceptance criteria, with its 90 degree requirement.
>
> In all fairness to Kathy. We get see this weird stuff because
> we are an independent lab. In fact, there is very little
> difference between IPC-A-600 Class 2 and 3 requirements.
> Generally the differences would not be observed at the solder
> connection.
>
> Your final question is the real question. Why Class 3.
> 1. Mission Critical Applications. Class 3 allows less
> variation in process output. Less variation means better
> control. Better control means less Murphy. 2. Harsh
> environments. The thicker solder fillets may withstand the
> rigors of harsh environments. (Assembly) 3. When your product
> lives in a glass house and you cannot tolerate cosmetic
> variation. (Assembly)
>
> BTW if you want Class 3 better start with IPC-2221, D-279 and
> SM-782 (Design).
>
>
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]] On Behalf Of Dobbs, Marie
> > Sent: Tuesday, December 30, 2003 9:51 AM
> > To: [log in to unmask]
> > Subject: [TN] IPC Board Quality
> >
> >
> > I am looking for your opinions and experience.
> > IPC has the 3 levels of classification for the Acceptability pf
> > Electronic Assemblies, and IPC also offers 3 levels of
> classification
> > for the fabrication of Printed Circuit boards.
> >
> > My question is this- Can I purchase a Class 2 Fabricated Printed
> > Circuit Card, and Expect to get Class 3 Workmanship Solder
> Joints from
> > Manufacturing Wave Soldering and Employee Hand Soldering?
> >
> >
> > One additional question, Other than the Military and NASA,
> what kinds
> > of products do you feel require the guidelines of a Class 3
> Board and
> > or Assembly.
> >
> >
> > Any input is greatly appreciated.
> >
> > Marie A. Dobbs
> > Training and Development Specialist
> > 100 Technology Drive
> > Westminster, MA 01473
> > Phone:  1-978-731-6827
> > Fax:  1-978-731-6950

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