Resistor sizes

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Are the smd resistor sizes defined in some standard somewhere? E.g. 0603, 0805.
Some manufacturers' dimensions vary from others. I want to know what is the actual standard size.
I would like to just buy from the big names like vishay or rohm but some resistors from china are very cheap for very small quantities.

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SMD resistor sizes are standardised.

Initially the sizes were driven by IMPERIAL or English dimensions expressed in thousands of an inch.
Then the more sensible METRIC sizes became available so that now we run the risk of stating an Imperial sized component and it could be misconstrued that we are quoting Metric size.

Google and Wiki are a good initial reference.

Note that a particular size of component may have more than one footprint when it comes to PCB artwork. In general choice of footprint will be driven by soldering process ( wave soldering versus reflow process )

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From the datasheets of Panasonic and Vishay for example, I get these values for 0805 resistor:
L x W
Panasonic >> 2+/-0.2, 1.25+/-0.1
Vishay >> 2.1+/-0.2, 1.25+/-0.2

I was hoping to find an actual standard that dictates what these sizes are supposed to be e.g. ANSI or IEC.

Quote:
In general choice of footprint will be driven by soldering process

Interesting, I do not know this. I just use the provided library footprint of my pcb software.

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midea,

In general I assume that anything made in China is of substandard quality, low-reliability, and has unpredictable repeatability of supply. Sorry, but that's been my experience for many years now.

Many non-Chinese brands use materials and components which have their origins in China. Some of these brands keep careful control of their Chinese made materials, components and sub-assemblies, so as to maintain their own high reputations.

Our present day world is flooded with CCC ( Cheap Chinese Crap ) and we must live with the consequences of that situation on a daily basis. The only thing you can do as an individual is to minimize your exposure to it, to the extent you can control it. Buying Vishay & Rohm resistors rather than Blew-Too-Soon CCC brand is one way to achieve this.

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Yes, I worry about expecting thousandths and getting millimeters or vice-versa. Look close when you're ordering.

I find 0603 (60 x 30 thousandths) pretty easy to work with. Mistakenly got 0402 size capacitors a while ago. Wow, those things are nearly small enough you have to consider quantum mechanics in placing them. 0803 parts are easy.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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Inductors seem, more often, to be sized metric.

Now, I always take care to check the product spec sheet and review the foot print in addition to all the other specs.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Good thinking. Sounds like experience talking.

I used to amaze people by reading the little blue book about some part, ordering a couple, designing a board and making it work. Somehow, those little blue books are missing these days.

"It's impossible to make a floppy disk interface for our system."

"Well, here's a little blue book from Western Digital that says how to do it?"

And thus was born, "The Impossible Disk Interface." Those old 8 inch floppies with big AC motors, huge flywheels and the little "digital compensator circuit" were fantastically reliable.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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Torby wrote:
Those old 8 inch floppies with big AC motors, huge flywheels and the little "digital compensator circuit" were fantastically reliable.
The good old days when floppies really flopped.

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Users of Apple and similar computers with the "mini" floppies always worried, "Isn't there some way to keep them from spinning all the time?" They were made for that. Would spin for years.

One day, a rather angry guy came storming into the lab. "THESE *(&(*& things are no good. The (&(*& floppy drive won't work." (He wasn't happy that we got the project to build the machines.)

"I'll go look at it," said the other Tom.

A while later, the angry guy was back. "HOW THE (*^&* DID THE DISK HEAD GET INSTALLED BACKWARDS?" The disk head was backwards? "THAT'S WHAT THE OTHER TOM SAID. SOMEBODY'S GOING TO GET CANNED FOR THIS!" (Canned: American slang for sacked.)

The machine had been running for weeks.

So, I let him drag me out there, where the other Tom was waiting. "What's this about the disk head being backwards?"

"Disk head? No, the diskette. He'd put the diskette in backwards. It's all working now."

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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So, how did we get from tiny modern resistors to gigantic antique disks?

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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Torby wrote:
Yes, I worry about expecting thousandths and getting millimeters or vice-versa. Look close when you're ordering.

It's really a crazy situation. They couldn't come up with some way to differentiate "0603" (imperial) from "0603" (metric)?

Quote:
I find 0603 (60 x 30 thousandths) pretty easy to work with.

Same here. Piece of cake.
Quote:
0803 parts are easy.

Not for me. I can't find them anywhere...

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midea31 wrote:
Quote:
In general choice of footprint will be driven by soldering process

Interesting, I do not know this. I just use the provided library footprint of my pcb software.

You'll even find that different manufacturers (and PCB houses) recommend slightly different footprints for the same size part e.g. 0603. I discovered that the default resistor footprints that came with my PCB package were huge, and could be reduced by a considerable amount to match those recommendations.

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kk6gm wrote:
Torby wrote:
Yes, I worry about expecting thousandths and getting millimeters or vice-versa. Look close when you're ordering.

It's really a crazy situation. They couldn't come up with some way to differentiate "0603" (imperial) from "0603" (metric)?

Quote:
I find 0603 (60 x 30 thousandths) pretty easy to work with.

Same here. Piece of cake.
Quote:
0803 parts are easy.

Not for me. I can't find them anywhere...

Agreed. That is just about the craziest thing ever.

Four legs good, two legs bad, three legs stable.

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Ok. I found this document IPC-SM-782 which tabulates what the standard sizes of the resistors should be.
It also gives a recommendation on the sizes of the land patterns.