SMT Beginner: Cap Polarity Band

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DocJC
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Posted by DocJC: Thu. Oct 2, 2008 - 09:54 PM
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I'm working on my first SMT board, trying hard to teach an old dog new tricks...

I have an 0805 10 uF electrolytic capacitor. As if 1206 isn't small enough for a beginner, but thats how this part came.

It is a small rectangle with a tin cap on each end to solder, and a dark band marking one end.

The data sheet, Here , (Mouser, AVX TACmicrochip Standard Microchip), has a nice diagram, clearly illustrating the polarity band, and that it is not to cross the center line for the part.

Only question is I don't see anywhere where it states that the polarity band marks the Positve or the Negative end of the cap.

Help!

Thanks,

JC

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Learning and Information, General Electronics
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bwall
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Posted by bwall: Thu. Oct 2, 2008 - 10:02 PM
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The band usually represents the anode(Positive).

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microcarl
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Posted by microcarl: Thu. Oct 2, 2008 - 10:24 PM
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Doc, The polarity band on SMD capacitors is positive - unlike that of the band marking the cathode on a diode.

Looking at that data-sheet that you linked me to, those are Tantalum capacitors, and the polarity band would designate the positive connection.

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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DocJC
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Posted by DocJC: Thu. Oct 2, 2008 - 11:05 PM
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Bwall and Carl,

Thank you both! Its amazing the little things that can pop up on a new project.

Now its back to work!

JC

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microcarl
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Posted by microcarl: Thu. Oct 2, 2008 - 11:09 PM
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DocJC wrote:
Bwall and Carl,

Thank you both! Its amazing the little things that can pop up on a new project.

Now its back to work!

JC

Pictures, pictures, we want pictures... :lol:

Great looking PCB boards, those DDS boards are. :wink:

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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jaydhall
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Posted by jaydhall: Fri. Oct 3, 2008 - 12:59 PM
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http://www.avx.com/docs/masterpubs/tantniob.pdf

Page 177

WA6MOK

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DocJC
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Posted by DocJC: Fri. Oct 3, 2008 - 04:16 PM
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jaydhall,

Thank you.

In my through hole parts I have some caps where the marker is for the + side, others where it is for the - side, so I wanted to check. Still odd that the data page on the cap defines the marker, but not which polarity it's marking.

JC

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kmr
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Posted by kmr: Fri. Oct 3, 2008 - 04:24 PM
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DocJC wrote:
Still odd that the data page on the cap defines the marker, but not which polarity it's marking.
While there is an industry standard for the marker as you have been told, I'd consider your example a deficiency in the datasheet.

Kevin Rosenberg
http://b9.com
http://kevin.hypershots.com

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jaydhall
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Posted by jaydhall: Fri. Oct 3, 2008 - 06:03 PM
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The main issue in this case is that the people who make the part and the catalog and the people who allow the catalog to be displayed on the web do not talk. This part, for example, shows up as two pages in the catalog. On page 177 is the information needed to distingush what the band means. The people who display the "data sheet" (two pages of the large catalog) do not know that it might say "see page 177 to understand the band", so you do not see it. The full catalog in your hand or a PDF would get you the information after you page through it. So, if it were a data sheet and not just two pages of a large catalog, I would agree that it is a deficiency in the data sheet. In this case it is a deficiency in displaying the correct full information needed. :)

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