George:

J-STD-001A is not a design standard. It does, as you noted, refer to 
various design and fab specs. This is because the task group that wrote 
J-STD-001A is keen to the fact that correcting design flaws during 
assembly operations is the WRONG way to make a PCB assembly. 

In the development of J-STD-001A, the task group looked hard at what 
requirements were assembly and what were design or fab (and belonged 
elsewhere). There are certain areas (electrical spacing is one) in which, 
say, the proximity of leads to one another or to adjacent lands may 
violate the design requirements. Using that example, the task group felt 
that there was no reason to repeat mounds of information on electrical 
spacing. Therefore, they simply refer back to the industry consensus 
design standand, in this case IPC-D-275. 

Besides the concept of "jurisidiction," there are other reasons not to 
repeat requirements from spec to spec. In the case of a typo, the mistake 
gets carried like a virus from document to document, until the whole 
industry is confused.

An example: In J-STD-001A, conformal coating thickness tolerances
are listed in 10.1.2.1. Unfortunately, these were picked up 
from IPC-D-275, which has incorrect tolerances. (IPC-D-275 mistakenly 
converted the requirements from MIL-STD-275E.) IPC-CC-830, the conformal 
coating qualification spec, has the correct tolerances. Had the task 
groups for D-275 and J-STD-001 simply referred to the CC-830, the problem 
never would have occurred.

(For the record, both specs have been corrected via amendment. Amending 
documents is much more time-consuming and expensive than simply getting 
it right the first time, of course.)

On the question of whether referenced specs are requirements: It depends 
on the verb modifier. The definitions vary slightly from document to 
document, but for J-STD-001A, all classes must adhere to "must" 
requirements. In 3.4.1, the design must be based on D-275, or the user 
must approve something else to use. 

Section 5.0, which covers components, uses "shall" instead of "must," 
which means it is mandatory for class 3, but if industry-accepted SPC is 
in place and documented manufacturers of class 1 or 2 product aren't 
bound by the requirement.

J-STD-001B is even more streamlined. It doesn't specify what spec 
manufacturers need (to comply with section 5.0), it simply says the 
components selected must be 
compatible with all materials and processes, and that evidence of this 
compatibility shall be maintained for review.

Mike Buetow
IPC Technical Staff
2215 Sanders Road
Northbrook, IL 60062
P: 847-509-9700, ext. 335
F: 847-509-9798
[log in to unmask]



On Fri, 26 Jul 1996, George Franck X2648 N408 wrote:

> Good Morning
> 
> Requirements question.
> 
> A customer requests that designs "meet the requirements of
> ANSI-J-STD-001A-1995 for preparation and soldering of electrical
> connections."  [Assume Class 2.]
> 
> Question:  In the above statement, are there any PWB Fab requirements,
> design or acceptance ?
> 
> What I found:  In J-001 there are references to IPC-D-275 and IPC-RB-276.
> References I found are: inside front cover, 2.1.2, 2.2.1, 3.4.1, and 5.0.
> 
> Point of confusion:  My gut tells me there's gotta be a call out in here
> somewhere, but these references do not look like requirements to me, they
> look like general information.
> 
> Thanks for you help
> George Franck
> 
> 
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