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I was recently looking at some SPI SRAM chips at Mouser and noticed that a particular IC came in both a SOIC-8 and TSSOP-8 package. The specs seem identical but the price is different (not by much, but different).

Visually, it looks like you could take a SOIC and push down from the middle to flatten the pins out and you would have a TSSOP. I know it's not the same thing but it looks like you could. ;-)

Anyway, given the same specs, why would you choose one package over the other? Both seem to be as easy to solder as the other (pins not under IC). Both seem about the same size.

For me, it would seem you would pick the cheaper of the two but there has to be more than that.

Thanks

EDIT

One thing I didn't make clear, is that I am wondering if the differences are just physical or are there others? I see now that the size difference can be quite large considering....

So I am gathering that if board space is a premium (which it usually is) then use TSSOP. But then why do we need SOIC at all?

Hope that makes it more clear.

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    \$\begingroup\$ Why the downvote??? \$\endgroup\$ – cbmeeks Jul 10 '15 at 17:29
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    \$\begingroup\$ Research required first. If unsuccessful, you may post here. \$\endgroup\$ – Leon Heller Jul 10 '15 at 17:33
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    \$\begingroup\$ @LeonHeller OP mentions in the question "specs seem identical". \$\endgroup\$ – Null Jul 10 '15 at 17:37
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    \$\begingroup\$ I think this is an interesting question for a general IC choice. +1 \$\endgroup\$ – Null Jul 10 '15 at 17:38
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    \$\begingroup\$ I'm voting to close this question as off-topic because of insufficient preliminary research. \$\endgroup\$ – Nick Alexeev Jul 10 '15 at 18:00
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The SOIC is more than 50% longer than the TSSOP. (4.9mm vs. 3.0mm) and only a bit wider. That may not seem like a lot to you, but on a crowded board it might make a difference.

The SOIC is taller (1.75mm vs. 1.2mm) which is enough to make a difference in a thin product.

The lead pitch is much closer (almost half) on the TSSOP- 0.65mm vs. 1.27mm, so for crude manufacturing processes the SOIC might well be preferred. If you think they are the same to hand solder- give it a try, unless you are quite skilled you'll see quite a difference.

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  • \$\begingroup\$ I prefer soldering TSSOP. Unlike SOIC, the pin pitch is small enough to use the drag method. \$\endgroup\$ – Matt Young Jul 10 '15 at 17:41
  • \$\begingroup\$ @MattYoung I can hand solder SOIC without using wick. I have to use wick with TSSOP. Hard to say which is faster I guess. \$\endgroup\$ – Spehro Pefhany Jul 10 '15 at 17:45
  • \$\begingroup\$ I think it all depends on your setup (iron, other tools), hand stability, etc. My 25-year-old iron can do SOICs without an issue, but I'd need a better tip if I were to solder TSSOPs \$\endgroup\$ – DerStrom8 Jul 10 '15 at 17:47
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    \$\begingroup\$ The way I do it only involves plenty of flux. Place the part on the pads and tack down the corners as usual. Apply flux to an entire side of the IC. Starting at an end, heat up a corner pad and add some solder. Once it flows, drag it along the entire row of pins, adding solder as needed. If you do it right and don't apply too much solder, you should be beautiful fillets on each pin. But I'm also the weirdo that prefers a conical over a chisel tip... \$\endgroup\$ – Matt Young Jul 10 '15 at 17:50
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    \$\begingroup\$ @MattYoung So the surface tension helps.. worth a try. Thanks for the 'tip'. I guess you're using 63/37 and not the gummy RoHS stuff.. \$\endgroup\$ – Spehro Pefhany Jul 10 '15 at 17:52
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TSSOP pin pitch: .635mm SOIC pin pitch: 1.27mm

As you said, they don't seem to be different other than in size. You are correct, size is really the only distinguishing factor. But, consider how modern electronics are always trying to be smaller, faster, and lighter, and you can see why one would use something like TSSOP, or even things like WL-CSP or BGA packages in their designs.

Lastly, TSSOP is somewhat harder to solder by hand than SOIC, but if you're careful, it shouldn't be too hard.

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  • \$\begingroup\$ That makes sense on the size and board space. But, wouldn't both be close to the same in difficulty when soldering? If so, then why use the larger SOIC at all? Just curious. \$\endgroup\$ – cbmeeks Jul 10 '15 at 17:48

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