SOJ-36 vs TSOP-44 for SRAM

[cbmeeks]

Assuming similar characteristics in design, why would one choose an SOJ-36 vs TSOP-44 package format for something like an SRAM component?

Again, assuming the same size SRAM, speed, power, etc.

SOJ-36 looks a little more compact but isn't really that big of a deal? Both are tiny to my old eyes.

Thanks for any input.

[BigEd]

Looks to me like TSOP is smaller and also much thinner, but a finer pitch. So, you might choose it for thinness (unlikely to be an issue in hobby land) or you might choose SOJ for the coarser pitch, which might make it easier... except, soldering TSOP must be easier because you can get to the leads, and with SOJ you can't. I think Garth has said he's sometimes bent the leads of an SOJ to turn it into something more solderable.

[cbmeeks]

That's a good point. The TSOP looks to be easier to solder despite the thinner profile. How are SOJ's soldered to boards typically? Or, are they not very common for hobby projects?

[BigDumbDinosaur]

cbmeeks wrote:

That's a good point. The TSOP looks to be easier to solder despite the thinner profile. How are SOJ's soldered to boards typically? Or, are they not very common for hobby projects?

I used an SOJ32 SRAM in POC V1 and manually soldered it.

POC V1 w/SOJ32 SRAM

POC V1 also has an SOIC24 package. which is near the left end of the board.

Garth's 4MB DIMM is built up from SOJ36 SRAMs, which he manually solders. POC V2 has two SOJ36 SRAMs that were manually soldered.

SOJ36 Manually-Soldered SRAM

TSOPs can be manually soldered as well. This video gives a good explanation of manual SMT soldering in general.

[cbmeeks]

That's funny because I was literally looking at that picture a few minutes ago for another topic I'm researching.

I guess I'm confused on the benefits of SOJ at all. Other than the pin spacing?

I should be able to solder either one. I have a pretty good magnifying lamp and I can solder 805 resistors without too much trouble.

Anyway, if you were to create POC3 (or 4?) would you still use SOJ?

[BigEd]

My guess would be that SOJ was among the earlier ideas for SMT - it's rather like DIP, but modified. Much more robust in handling than the likes of TSOP, too.

[BigDumbDinosaur]

cbmeeks wrote:

I guess I'm confused on the benefits of SOJ at all. Other than the pin spacing?

SOJ packages, such as PLCCxx, can be socketed, which made them attractive back in the days when reflow soldering was not as common and as reliable as it is now. If memory correctly serves me, the SOJ package form has been around since the late 1970s, and was one of several package forms originally standardized by the old EIAJ and subsequently adopted by JEDEC.

Quote:

Anyway, if you were to create POC3 (or 4?) would you still use SOJ?

Yes. At this time, the largest SRAMs that are available that operate on 5 volts are 512KB parts in SOJ36 packages.

[BigDumbDinosaur]

Incidentally, Wikipedia has a reasonably good article about SO packages in general.

[GARTHWILSON]

BigEd wrote:

except, soldering TSOP must be easier because you can get to the leads, and with SOJ you can't. I think Garth has said he's sometimes bent the leads of an SOJ to turn it into something more solderable.

It must have been someone else. The only thing I have bent SOJ leads for was to make them more like a DIP so I could stack 8 SRAM ICs in my first attempt at a 4Mx8 SRAM module. I decided it wasn't worth it. The module I sell uses the SRAM SOJs without bending the leads. The soldering iron touches the pad and the lead at the same time, heating both, and I shove the solder in there, bridging the whole side. Then I hold it vertically and go from top to bottom with the iron, and all the excess stays on the iron, not the board. Each pin is left with just the right amount of solder, with no bridging, as shown in BDD's second photo above, of his POC V2 (he did his POC V1 himself), the photo of the 36-pin SRAM SOJs I soldered for him with a 1/8" chisel-tip iron. I shake the excess solder off the iron. Yeah, that's kind of wasteful of solder; but it's a negligible expense.

[Dr Jefyll]

GARTHWILSON wrote:

It must have been someone else.

I'm the one. It took me a while to find where I'd posted this! But it's on page four of Techniques for reliable high-speed digital circuits.

There's lots you can do with J-leads -- I'm quite comfortable with them (and the .05" spacing). But be sure your soldering iron is one with a fairly fine, conical tip. Chisel-shaped tips are not what you want.

I've also worked with the packages with finer pitches (below .05") but the soldering technique is different. Rather than soldering individual pins, you flood ALL the pins with solder then remove the excess. It's not terribly difficult, except that stuff that small is so darn hard to see !