ET-3400 ROM - SO what ?

In order to speed up the PCB layout process, I have copied another PCB layout I used for a similar ROM replacement PCB. This new project also has an SOIC-14 that the other one didn't.

I've only used SMD components a few times so far and the PCB application has numerous libraries that I am still struggling to find things in. I think some of the library entries are merged from an older version of the application I am using, so there are some custom ones mixed in there that I drew myself previously. It's a bit of a mess.

I found the SOIC-28 footprint for the 28C64B on the last project and that was called SOL-28 so that one was OK to re-use, but now I need an SOIC-14 for the 74LS20 dual 4-input NAND gate. At least that's what the supplier states it is. The data sheets show slightly different naming, so I'm going to have to check the dimensions.

I looked for a SOIC-14 in the library and find that there are a number of different but similar sounding and looking components and I'm not familiar with them all or which one is correct. However there is no SOIC-14 instead I found:

SO14, SO-14, SOJ-14 and SOL-14.

OK, I give in, which one is it ?

I decided to place one of each onto my drawing and compare them the the actual data sheet for an SOIC-14, and not surprisingly none of them match perfectly and some are way out.

So I have to draw up a new one, and I am struggling to use the component editor in this newer application. I'm used to the old one and it takes a while to teach an old dog new tricks.

Anyway I drew up a layout according to the data sheets alongside the ones I found in the library and while two are close (SO14 and SO-14), the is no cigar.

Here is the wide variation of SO packages I found next to the one I drew.


I could probably have use the SO-14 version (middle one) and adjusted the pad sizes, but so I don't run into this confusion in the future I've added the SOIC14 (left hand component) to my local library and that's the one I'll be using. Maybe.

I think that before I get any PCB's made I'll have to order some of the 74LS20 SOIC-14's first just to be 100% sure of the size.

back to the PCB layout...

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