Hi Jeff,
I believe that no stress relief is bad because you do not want to have the component under tension in the assembly where it could be affected by any shock (thermal, mechanical, etc) or vibration incident. Equate this to stringing a guitar...we want to keep tension off of the string/leads to prevent the reverberation that would occur if it were to get "strummed".
I believe the intent with having a minimum of 1 lead diameter (but not less than 0.8mm) of spacing from the edge of the component body/bead/weld is to prevent stressors from being applied directly to that termination on the component that would end in the eventual fracture or weakening of it. Simply by having this spacing and by following the table describing the minimum bend th lead radius described in the standard, you would have formed adequate stress relief for most cases...the addition of loops in various forms may be required for specific scenarios, but that should be detailed in procurement docs and not assumed by the manufacturer.
In summary, these 2 items are very closely related, but are in place for different reasons. By having stress relief in the lead, we have slightly reduced the chances of an improperly formed lead (bend radius started too close to body) causing an incident in the field...hence it's required for Class 2,3.
I hope that this helps.
Don McFarland
Sent from my iPhone
On Jan 27, 2011, at 4:58 AM, Jeff Popp <[log in to unmask]> wrote:
> In the 610 -rev E, clause 7.1.2.2 on page 7-9 deals with lead forming and stress relief. The first criteria mentions lead bends less than 1 lead diameter away from the body being only a process indicator for Class 2. The criteria directly below that calls No stress relief a Defect for Class 2.
>
> It seems a little contradictory to me. If you place a bend less than 1 lead diameter away from the seal, is that really any different than no bend whatsoever? It seems to be splitting hairs and from a practical standpoint, a little difficult to tell the difference.
>
> Any thoughts?
>
> Best Regards,
> Jeff
>
> Jeff Popp
> Quality Assurance Technician
> Compunetix, Inc.
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