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

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------