Phil,
I offer the following from our workmanship criteria for space quality
hardware:
Cement fillet on both sides of component.
Length of Fillet to be minimum 80% of body length.
(need not be continuous)

Width (W) of fillet (on each side of the component) within ½ D to 1 D
        (D is the component body diameter)

Height (H) of fillet visible to a maximum ¾ of the component body radius.

There is no measurable minimum height, but if you meet the other size
criteria, the height will normally take care of itself when the adhesive is
applied.  I feel any bond that is more than half-way up the body constitutes
encapsulation, not bonding, and excessive for your purposes (unless the
material is VERY compliant).  We have never had a failure with the above
criteria (provided there is adhesion to component and board).

Hope this helps,

R. G. Blomberg
Honeywell - Space Systems
Staff Production Engineer
(727) 539-5534 voice
727-539-4469 Fax
[log in to unmask]



-----Original Message-----
From: phil bavaro [mailto:[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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