Phil,

So does that mean that if your house is still standing after the earthquake,
but the foundation is cracked, that it is OK to move right back in? I
wouldn't think so.

If the bonding has cracked and broken, it is a structural failure.
Electrical failure is probably just around the corner. Reducing the amount
of adhesive as a means of reducing cycle time doesn't seem correct as you
have already established how much adhesive is necessary to hold down the
parts.

If cycle time reduction is the motivation behind what you're trying to
accomplish, the entire assembly process should be studied for possible
restraints throughout the entire process. I think the objective should be to
try build what you're already making in a shorter time period before making
changes to the acceptance criteria as a means of cycle time reduction.

Bill Kasprzak
Moog Inc.

> -----Original Message-----
> From: phil bavaro [SMTP:[log in to unmask]]
> Sent: Monday, March 20, 2000 5:05 PM
> To:   [log in to unmask]
> Subject:      [TN] Electrolytic Capacitor Staking Requirements
>
> OK, I know, I know. Why is anyone still using thru hole parts which have
> to
> be bonded to the board......!!
>
> Well. all I can say is that we are and the question I have for this group
> is what are the requirements for how much and how high.
>
> Here's the background info:
>
> An automotive electronics circuit card has about seven very tall
> electrolytic caps on it which need to be secured to the board so that the
> vibration does not sever the two leads on these parts.  Historically I
> have
> always asked that these be bonded 360 degrees around the perimeter and a
> minimum of 50%, up to a maximum of 100% of the height of the part using a
> thixotropic UV cure adhesive.  This way the part could not bend or move at
> all.
>
> Using this criteria, I have never seen a failure as a result of the
> bonding.
>
> Here's the problem:
>
> A new engineer decides to minimize the adhesive amount (due to cycle time
> of course) so that just it connects the board and the bottom of the part
> only (maybe as high as .15" total which only allows about .10" of contact
> to the body of the part.  These parts are .75" tall.  The new engineer
> feels justified because the products which were bonded this way made it
> thru a HALT test exposure without electrical failures.
>
> I look at the assemblies which are supposedly OK and find that the
> adhesive
> has broken loose from the pwb on at least five out of the seven parts and
> what is remaining on the parts have fracture lines as well.
>
> I consider this condition unacceptable and feel that after environmental
> testing, adhesive bonding should remain intact 100%.
>
> Am I right or should I yield since the assemblies made it thru the HALT
> testing?  What bonding requirements do you impose for these type of parts
>
> All comments are welcome.
>
>
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