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I'm pretty new to this SMT stuff, and I'm looking at resistor arrays.

From what I can see on my main supplier's website (RS) most of the SMT arrays are of a package type '1206'.

Now, my PCB layout package (gEDA PCB, yes, I use Linux) has a footprint for 1206, but it seems to only be a single pair of pads and not the 8 pads that the arrays would need.

Do you think this is an error in the PCB package, or is the 1206 'package' just \$\frac{1}{4}\$ of the actual package and I'd need to place 4 footprints at the right spacing?

Specifically this is the product I am looking at: http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=4351807

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  • \$\begingroup\$ It's usually best to refer to the program you know as 'PCB' as gEDA PCB. Trying to find documentation without knowing that it's a part of gEDA and without the URL (pcb.gpleda.org) is difficult. \$\endgroup\$ Jun 29, 2011 at 1:15
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    \$\begingroup\$ @Downvoter - Why? If you're trying to say that the question does't show research effort, I'd argue that most questions on the site could be answered by reading the datasheets, and the footprints can be one of the hardest parts of those datasheets! The preponderance of 1206 single resistors could easily cause confusion when used in reference to an array. Finally, not everyone is familiar with (or has access to) IEC 60115-9! \$\endgroup\$ Jun 29, 2011 at 2:49
  • \$\begingroup\$ @Kevin: I don't have so much of a problem with "read the datasheet for me" questions, but at least include a link to an example part. \$\endgroup\$
    – W5VO
    Jun 29, 2011 at 8:04
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    \$\begingroup\$ Re IEC60115-9: all those standards organizations, like ISO and IEC are crooks! They charge for membership, for voting rights, and then they charge for delivering information. You would think they would be glad to have the widest dissemination possible if they want their standard to be adopted. \$\endgroup\$
    – stevenvh
    Jun 29, 2011 at 8:48
  • \$\begingroup\$ @stevenvh The worst is the USB consortium... extortionists! \$\endgroup\$
    – Majenko
    Jun 29, 2011 at 9:20

4 Answers 4

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The libraries in the official distribution are not very extensive. The gEDA way is to find/create your own, you'll likely have your own personal preferences about pad lengths, symbol sizes, silkscreen formatting etc. There are no resistor arrays in the default libraries to my knowledge.

1206 is a common large SMT resistor package, as you guessed. It refers to a 120 mil by 60 mil rectangular package. Some newcomers to SMT prefer to use individual 1206 components, but most use 0805 (80 by 50 mils...you get the idea) for general resistors that have to be hand soldered. I like 0603, personally, but I like to solder under a binocular microscope.

However, in automatic soldering, it's also a popular outline for arrays: the 4 resistors fit in a space 120 mils by 60 mils. You'll also find them in 0805 and 0603, but you'll want to stick with 1206 if you're new at this. After peering into my crystal ball, I'm guessing that you might be looking at a page on RS like this and datasheets with packages like this:

package

...and footprints like this:

footprint

You need to draw the second image as a footprint in PCB, using the dimensions in the table.

Some parting thoughts:

  1. Ideally, you'd use a stencil and reflow these components. However, 4 resistors in 1206 isn't too bad with an iron: It's only a 50 mil pitch, it gets dicier once you start looking at 0.5mm pitches.
  2. Especially for reflow, you'll probably want the concave configuration to wick the solder away from the other pins and minimize bridging. For SMT arrays, concave means that the solderable surface is inside, on the round part of the castellations, while convex means that the castellations cut through the conductive flat edge of the component. This may make it more difficult to heat up if you're going to be using an iron, but it takes up less space, because the pads are partially under the component.
  3. They're quite cheap, get some test parts to see what's easier to solder and double-check your footprints by printing out on regular paper.
  4. If you're worried about solder feasibility, here's a story that should bring you hope: My most-difficult rework job was soldering 36-gauge wires from pin 1 to pin 5, pin 2 to pin 6, and pin 3 to pin 4 of the footprint of an 0603 3-circuit ferrite bead. 1206 outline 4-circuit packages should be fairly easy in comparison...
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  • \$\begingroup\$ Yes, I'm looking at concave and reflowing - I'm thinking of making my own reflow oven. \$\endgroup\$
    – Majenko
    Jun 29, 2011 at 8:22
  • \$\begingroup\$ @Matt Jenkins: concave is indeed better for reflow, while convex is better for manual soldering, because the connections-pads look more like pins on a QFP. The need a few square nanometers more space. \$\endgroup\$ Jun 29, 2011 at 10:04
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The package is whatever the datasheet says it is. Cramming a bunch of resistors into a 1206 package sounds rather tight, but I suppose is possible. That would make the pin pitch rather small though.

Possibly someone at the distributor did a cut and paste and forgot to change the package type. In any case, LOOK IN THE DATASHEET. All we can do here is speculate, especially since you haven't provided a link.

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  • \$\begingroup\$ The data sheet gives dimensions, which is all very well when you have a clue as to what '1206' is meant to be (I now know thanks to other answers0. \$\endgroup\$
    – Majenko
    Jun 29, 2011 at 8:23
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    \$\begingroup\$ @Matt, I still don't see a datasheet. You now give a link to the distributor page, but that's not a datasheet and I don't see a obvious link there to a datasheet. The real datasheet should give mechanical information without you needing to know what a 1206 package is suppsed to be. In fact I wouldn't rely on what I think a 1206 package is in any case. I want the datasheet to tell me exactly what the real dimensions are. No need to get snippy, by the way. That will only get you less useful answers in the future. \$\endgroup\$ Jun 29, 2011 at 12:07
  • \$\begingroup\$ It's there, under "Technical Reference". I'd link to it, but it's a stupid javascript thing. Search the page for "Data Sheet" \$\endgroup\$
    – W5VO
    Jun 29, 2011 at 12:40
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    \$\begingroup\$ @Matt: After W5VO pointed me to the datasheet at docs-europe.electrocomponents.com/webdocs/0114/… (now why couldn't you do that), I found the dimensions spelled out in detail on page 5. You don't need to know anything about a 1206 package or any other. All the dimensions are right there. \$\endgroup\$ Jun 29, 2011 at 14:28
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In the case of a resistor array, 1206 describes the size of the package, and does not imply a pin configuration. 1206 sized single resistors have been around a lot longer that the arrays, so I would assume that the 1206 footprint is for a single resistor. Not an error, per se, but a case where a single resistor in a 1206 package is assumed.

You will need to make (or find) an appropriate footprint that matches the part datasheet.

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  • \$\begingroup\$ @Pete - the datasheet (or a related document) should give you recommended footprints. If it doesn't, find another supplier. \$\endgroup\$
    – stevenvh
    Jun 29, 2011 at 19:21
  • \$\begingroup\$ @steven - That's exactly what I said... the poster will have to make, or perhaps find in a library, an EDA footprint that matches the footprint information given on the datsheet. \$\endgroup\$
    – B Pete
    Jun 29, 2011 at 20:26
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SMD passive component packages like for resistors and capacitors are designated by their size in hundredth of an inch. A 1206 is 0.12 inch by 0.06 inch (3 mm by 1.5 mm). Today for single parts 1206 is only used for higher voltages or power; 0603 is more or less standard, moving to 0402. The smallest size is 01005, that's a surrealistic 0.25 mm by 0.12 mm! (I want to see that pick-and-place machine in action!)
The same designation is used for arrays of resistors/capacitors. So the 1206 refers to the total length and width of the array. The dimensions are not always the same as for the single components; 0805 is a single part package, while the 4 resistor arrays I use are 0804.

For your specific device, RS says it's a PhiComp (Yageo). On the Yageo website, when you select resistor arrays/networks you're guided to a parametric search, which will bring you to a datasheet.

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