Arshia Arvandi asked:

>Hello,
>
>        My name is Arshia Arvandi and I am a mechanical engineer at TTC and
>currently we are in the process of designing a power supply that has a
>transformer which weighs 2.16 oz. and we are  using 7 leads with divided out
>gives .308 oz p/lead.
>
>According to the IPC-D-319 standard, section 3.6.5, it states that, "all parts
>weighing .25 ounces or more per lead should be supported by specified means,
>which will help insure that their soldered joints and leads are not relied
>upon
>for mechanical strength."

The authors want you to use some other means than the solder joints and
leads to secure that big xfrmer. In the frame of reference of devices
mounted to PCB's, 2 ounces is huge.

>No where, that i have been able to find, does it give the size of the lead
>(these transformers have pretty big leads) in relation to the weight.

It's not simply whether the leads are strong enough to support the device.
No matter how big they are, you still have only the solder interface and
PTH copper in the hole walls to hold that transformer in place. If
vibration or shock occurs, the stress will concentrate, and that part will
probably break those PWB solder joints someday. Fatigue will be the failure
mode. Tin-copper joints are weak compared to typical leads.

>I would be very grateful if i could either get the answer to this question
>or be
>referred so someone who may be able to help me solve this mystery.

Who better to answer this than an M.E.? Think back to your strength of
materials and basic physics. Considering the design life, the board's
expected use environment, and how critical reliablity is, you will be able
to answer this. Most transformers have some mechanical mounting provision
other than the leads, i.e. the core or case will have holes or a bracket
you could secure to the board with appropriate fasteners. You can go for
additional physical integrity or hope for the best and take the easy way
out.

It depends on some many factors no one can "solve" this without knowing
more. I would say simply that if you don't use supplemental means of
securing the part, you are not meeting IPC-D-319. This may or may not be a
concern.

good luck,

Jerry Cupples
Interphase Corporation
http://www.iphase.com