No need to be so "why anyone" , me one of them, not feelin any shorter .
1
in short no, yo should NOT yield, surviving HALT hanging on one hair "pass"
is hardly the way .
Me the humble inquisitor would seriously question any HALT validation
procedure which would NOT include final visual.
It's clearly no pass, regardless of electrical pass ;
UNLESS the halt is an actual simulation life limit (which i doubt, from the
sound of it) .
2
One cure which i did on numerous designs (PS's main offenders)coping with
G's ;
spread those cans to more of lower ones, if you have the real estate and
budget .
Easy way out (still flooded!),
3
If you can't (likely),
than you have to lecture your keen freshling about basics of force vectors;
hopefully he's physically minded and will be able to understand that a TV
buried in sand is proportionally more stable and not prone to tipping over
to the depth of sink in (hate TV lately, endless bull, pardon the
reminiscence);
the force spread of vertical, diagonal and horizontal vectors in both
negative & positive/pull & push/adhesion & compression/ is not a rocket
science to calculate .
Been through this often enough, DO NOT BUDGE,
this relatively naive physics do account for a lot of recall disasters .
Funny part is the after recall "topping up" does have different signature
again,
remember once the top up layer not quite bonding working it's way out in no
time .
address the procedure (it's almost clearly wrong), than explanation (fault &
why = calculus),
than set the freshling from reinventing the wheel.
Feel with yo, have this "efficient" new age pupils paddling fast circles
around me all the time,
sometimes for years before they realize breaking ice is not for knockers .
Keep a diary , management 's got often selective RAM's .
cu paul
-----Original Message-----
From: phil bavaro [mailto:[log in to unmask]]
Sent: Tuesday, 21 March 2000 9:05
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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