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July 2011

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Subject:
From:
Victor Hernandez <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Thu, 14 Jul 2011 07:48:06 -0500
Content-Type:
text/plain
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text/plain (173 lines)
Fellow TechNetters:

   Are there any resistor gurus out there that can share process experience or provided reading resources?

Victor,

-----Original Message-----
From: Hernandez, Victor G 
Sent: Thursday, June 23, 2011 2:29 PM
To: Steven Creswick
Cc: Hernandez, Victor G
Subject: RE: [TN] Ceramic resistor coating

Steve,

   You brought up some good points on the trimming process that I was not considering.

Thanks,

Victor,

-----Original Message-----
From: Steven Creswick [mailto:[log in to unmask]] 
Sent: Thursday, June 23, 2011 1:59 PM
To: Hernandez, Victor G; [log in to unmask]
Subject: RE: [TN] Ceramic resistor coating

Victor,

Sorry, I glazed over on the moisture resistance.

It depends - used to be in hybrids that we would apply the
overcoat/glaze/glass before resistor trimming.  This would leave only the
walls of the laser trim kerf exposed to anything.  One could apply the
overcoat AFTER laser trimming, but then the resistor is subject to some
degree of drift.

Don't know exactly what the chip resistor suppliers are doing nowadays.  If
you look at some under a scope and you can clearly see nothing in the kerf,
then you know they cut through the glass.  If you see a depression in the
glass where the kerf is, then you know they applied afterwards.

It is glass.  I forget exactly what composition.  Can moisture get through
it?  Yes, slowly, but can also get at the resistive material via the laser
trim kerf faster.

The resistive composition is normally a fritted, ruthenium oxide based
compound.  Low ohmic values will normally be affected faster.

As I recall, the fired thickness is about 1/2-3/4 mil thick  [~50-75 µm]


Steve Creswick
http://www.linkedin.com/in/stevencreswick
                         616 834 1883




-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]] 
Sent: Thursday, June 23, 2011 2:10 PM
To: [log in to unmask]; [log in to unmask]
Cc: [log in to unmask]
Subject: RE: [TN] Ceramic resistor coating

Steve,

   Thank you for sharing.
You did not comment on the moisture inquiry.   I heard that moisture can
penetrate to the conductive ink and cause corrosion.   By the way how thick
is this coating or min requirement.

Victor,

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: Thursday, June 23, 2011 1:05 PM
To: [log in to unmask]
Subject: Re: [TN] Ceramic resistor coating

Victor,

Chip resistors normally have a low temp firing glass over the resistive
element, or sometimes an organic, epoxy based material.  You would
ultimately have to check with your supplier to determine which. .... or dig
at it [destructively] under a microscope to estimate for yourself.

The glass resistor covercoat normally fires at 500-525°C, so it will not be
bothered by much of anything which you can do to it.

The organic covercoat would act like a standard epoxy and could discolor,
change color, crack, peel, etc with excess temps, or could have issues with
solvents, etc.

Hope this helps


Steve Creswick
http://www.linkedin.com/in/stevencreswick
                         616 834 1883





-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
Sent: Thursday, June 23, 2011 12:16 PM
To: [log in to unmask]
Subject: [TN] Ceramic resistor coating

Fellow TechNetters:

   What are some typical ceramic resistor coating?   Are these coating
moistures proof/resistance?  Can the coating deteriorate with temperature?

Victor,


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