Here are the J-STD-001C references that seem applicable. Under the heading of  "Assembly Processes" 6.1.2.1 Lead Deformation Limits . . . Exposed basis metal is acceptable if deformation does not exceed 10% of the diameter, width or thickness of the lead.  IPC-A-610C 5.4.1 has the same acceptance criteria but adds a defect condition "Lead is deformed from repeated or careless bending". This one causes some discussion.

Under the heading of  "Assembly Requirements" 9.2.4.1 Exposed Basis Metal Exposed basis metal is acceptable on component lead ends and the edges and/or periphery of printed board lands and conductors.  IPC-A-610C 6.5.2 defines this condition as a Process Indicator for Class 2 and  3 products. Provided the component or copper on the substrate is not damaged beyond the acceptance criteria.

 This does not reflect a change in position going back to J-Std-001B. Paragraph 9.2.5.3 also stated that exposed basis metal at the ends of  leads or edges of copper conductors was acceptable. As for your question, Mel Parrish added information on this subject last week that, I believe, accurately reflects the consensus of the committees writing the document;  the exposed copper would not, in most service environments, corrode to the point of failure. That in environments that were likely to cause corrosion related failures, coatings or  perhaps encapsulants would be appropriate.  But then conformal coating is not required (by these standards) on the lead ends either.

I am not aware of data supporting the acceptance criteria. I'll snoop around a little, but I don't think we have it.

> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of
> [log in to unmask]
> Sent: Monday, May 06, 2002 1:39 AM
> To: [log in to unmask]
> Subject: Re: [TN] Wave solder re-runs/re-work exposed copper
>
>
> I may be out of date, Guy, or maybe there's a deficiency in IPC-A-610, but
> in the MIL Spec days, the law in my previous company was "there
> shall be no
> exposed copper", and the assembly process had the Wave Solder - Trim Leads
> - 2nd Wave Solder operations built into the Master Assembly Instruction
> documents (before the solder joint damage with this sequence was
> recognised).
>
> If exposed copper is now acceptable, what changed (class 3 boards I'm
> talking about)? Part of the reason for over-soldering exposed
> copper was to
> prevent the copper oxidising, and part of the reason was to prevent cut
> leads puncturing the conformal coating. Any modern info gratefully
> received.
>
> Peter
>
>
>
> "Guy Ramsey" <[log in to unmask]>  03/05/2002 07:10 PM
>
>              To: "TechNet E-Mail Forum." <[log in to unmask]>, DUNCAN
>              Peter/Asst Prin Engr/ST Aero/ST Group@ST Domain
>              cc:
>              Subject: RE: [TN] Wave solder re-runs/re-work exposed
>              copper