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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.

cbmeeks
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    That's exactly what I did. Just because I searched for something doesn't mean I always put in the correct search terms. Hence, I ask... – cbmeeks Jul 10 '15 at 17:34
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    You just had to look at the specs. in the data sheet. – Leon Heller Jul 10 '15 at 17:35
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    I'm asking in general. Not specifically to the IC's I found. Which is why I didn't list part numbers. – cbmeeks Jul 10 '15 at 17:36
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    @LeonHeller OP mentions in the question "specs seem identical". – Null Jul 10 '15 at 17:37
  • Look at the datasheet for SOIC-8 and TSSOP-8. It's not that hard to find the differences – DerStrom8 Jul 10 '15 at 17:37
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    I think this is an interesting question for a general IC choice. +1 – Null Jul 10 '15 at 17:38
  • SOIC: http://www.centralsemi.com/PDFS/CASE/SOIC-8PD.PDF TSSOP: https://www.ichaus.de/upload/pdf/Package%20dimensions%20MSOP,%20SSOP,%20TSSOP-A2.pdf (Scroll down to the section for the TSSOP). The differences are pretty darn clear – DerStrom8 Jul 10 '15 at 17:40
  • "Both seem about the same size" This is where you're wrong – DerStrom8 Jul 10 '15 at 17:41
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    Some questions can also be answered by datasheet. Majority of the datasheets have a dimensioned drawing for all IC packages that the chip comes in. – Nick Alexeev Jul 10 '15 at 17:46
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    @cbmeeks If converse you want, then to our [EE.SE chat](http://chat.stackexchange.com/rooms/15/electrical-engineering) better go. – Nick Alexeev Jul 10 '15 at 17:47
  • But think about it, if you're wondering about specific packages, then wouldn't it make sense to look directly at the package datasheets first, rather than asking here (or even doing a general google search)? Google searching is an art--You need to know how to do it properly in order to get the results you need. Try to avoid making general searches. – DerStrom8 Jul 10 '15 at 17:53
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    Is the datasheet going to tell me which to use in a project? Generally speaking? – cbmeeks Jul 10 '15 at 17:55
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    I'm voting to close this question as off-topic because of insufficient preliminary research. – Nick Alexeev Jul 10 '15 at 18:00
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    Comments are not for extended discussion; this conversation has been [moved to chat](http://chat.stackexchange.com/rooms/25713/discussion-on-question-by-cbmeeks-whats-the-main-differences-between-a-tssop-an). – Nick Alexeev Jul 10 '15 at 18:08
  • Yet another closed question that ranks highly on Google and that was very helpful. A vote to close often says more about the person voting than it does about the question per se. – Craig.Feied Feb 20 '23 at 04:46

2 Answers2

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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.

Spehro Pefhany
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  • I prefer soldering TSSOP. Unlike SOIC, the pin pitch is small enough to use the drag method. – Matt Young Jul 10 '15 at 17:41
  • @MattYoung I can hand solder SOIC without using wick. I have to use wick with TSSOP. Hard to say which is faster I guess. – Spehro Pefhany Jul 10 '15 at 17:45
  • 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 – DerStrom8 Jul 10 '15 at 17:47
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    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... – Matt Young Jul 10 '15 at 17:50
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    @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.. – Spehro Pefhany Jul 10 '15 at 17:52
  • Yes, I use 63/37 for everything I build by hand, can't really comment on how well it would work with any of the lead free options. – Matt Young Jul 10 '15 at 17:55
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    Here four years late but an important tradeoff I don't see listed here is that there are many mechanical issues with TSSOPs because of the reduced lead compliance. I encourage a reader looking here to consider if solder joint reliability is a concern in their design, and lean toward SOICs if so. – jalalipop Jun 24 '19 at 14:32
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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.

justinrjy
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  • 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. – cbmeeks Jul 10 '15 at 17:48