Struggling with custom chip / modifying generic IC


#1

Hi I’ve watched a few youtube vids on part design and read a load of online tutorials and guides and I’m getting nowhere still!

I have a 40 pin chip which is DIP with 20 pins at the top and 20 at the bottom. So I’ve tried the approach other users have done in their guides and such where you take a generic IC from Fritzing parts list, drag it in and then edit it.

It’s not working for me. For a start I can’t change the size of the IC. Mine is 26mm long and 11mm wide overall (including where pins come out to etc).

The closest 40pin IC I can get is Small (0.7mm/0.0275in) Generic IC DIP THT with 300mil spacing.

When measuring that generic IC it seems to be approx 10.4mm wide by 51 mm long.

I tried also opening up the svg in inkscape and have sort of squashed the graphic down smaller, but then the Parts Editor in Fritzing has no option to make the chip the right size there. It let’s me load in the new SVG but it dosn’t display right and goes massive within the current chip so that I can’t see it properly.

How the heck does one make a small DIP chip from a generic IC? It’s just a laptop ram chip and I’d hoped it wouldn’t be too hard to setup so I can make a small pcb for it?

Thanks for any help.


#2

Do you have a data sheet for the IC you are trying to make? Is it surface mount or through hole (the quoted spacing sounds odd for through hole)? You could also post the svg file here by renaming it from .svg to .fzpz (the forum sometimes has trouble rendering svg files) and telling us it is actually an svg. Upload is 7th button from the left in the reply tool bar.

Peter


#3

Hi thanks for reply and helping me out. Basically it is this RAM chip:

https://www.ebay.co.uk/itm/HY514260BJC-70-256k-x16-Bit-CMOS-Dynamic-RAM-40-Pin-Plastic-SOJ-Hyundai-1pcs-/263285847398

I don’t know if fritzing has a socket it can push into or something like that… I was just going to unbend each pin straight and solder with through holes in pcb. But whatever is easier works for me!


#4

Yep this is an SMD device, I doubt you will have much luck at trying to get it through hole although you could try. It appears to be .05 in spacing which is quite small. You might be able to hand solder it if you are good at SMD or have a hot air rework setup. This looks to be the soj package outline that you would need to do this. A suitable foot print is easy enough to make if you would verify that the pin spacing is indeed .05in or 1.27 mm

Peter


#5

They are 28mil pins on a 50mil spacing, and when you account for the hole there isn’t much gap between them to make much of a pad. I don’t think you can home etch this one, or if the unfurled pins will be long enough to go through to the other side of a PCB.


#6

Hi thanks yes it does seem to be 0.5mm, though only measuring with a ruler so hard to be exact. The fatter tops of the pins seem to be 0.5 apart but of course where they narrow out there is a wider gap.

Is there any kind of socket that I can use that will accept this chip, then I could just solder the socket to the pcb. And the component made in fritzing could then be for the socket instead?

Thanks again for any help :slight_smile:


#7

I don’t know if there is a 40 pin SOJ socket, but if you find one post a link to the datasheet.

The other thing I can think of is a SOJ to DIP adaptor board, so maybe look on Ebay.

FZ is very undermanned, and most people working on it are trying to fix it, so you will have to do the search work and bring it here.


#8

The question becomes can you solder a .5mm surface mount part? It is easy enough to make a footprint for this, it won’t be that easy to solder it down if you aren’t experienced with SMD hand soldering (as I am not). I’ve seen some amazing stuff done but I’m not sure I could do it.

Peter


#9

If you presolder the pads and legs, then add lots of flux before placing the part and then use a hot air station it would be easy to solder. Even easier with a solder paste.

If you have professionally made boards with solder resist then soldering with an iron using lots of flux and solder would work. You would just then use some solder wick after to clean up any bridges and lots of inspecting and touching up to ensure no bridging under the chip has occurred.


#10

OK here is a generic 40 pin 400 mil spacing IC (ready to have its pin numbers changed by you) with a 40 pin soj40 footprint from this site:

as the pcb footprint as always you would need to verify the footprint against the real part (because I don’t have one).

Generic_40pin_400mil_soj40_footprint.fzpz (11.2 KB)

I see to my surprise that there are cheap ~$2 US sockets available for this form factor. You may want to try one of them as a starting
point (I assume they are cheaper than the ram).

Peter


#11

I found some sockets but they looked like the same SMD 0.5mm pitch.


#12

Yes, but a $1.50 socket that you screw up while soldering is a lot better than a $24 ram chip :slight_smile: .

Peter


#13

Hi that’s great thanks. Sorry it has taken me so long to thank you and get back a reply on here.

The socket approach would be really good if possible. Do you know where I can get them from or what they’re called etc? Also how do I then add the socket to the PCB instead of the chip, would you be able to draw the socket as a part too? Maybe we can then add both the chip and the socket to a parts repo?

Thanks again :slight_smile:


#14

Just search for it in Google because we know as much as you.

Sorry we don’t do anything except very simple searches anymore because it takes us too much time.


#15

I didn’t keep the search term I used that turned up the $1.50 sockets, but a google search for “soj40 socket” turns up a bunch (one I looked at was $26 though, but there were 2 in the $1.50 range on my original search). They aren’t through hole sockets though, they are surface mount as well and would probably use the same footprint that I made (although I didn’t check). The possible advantage is that you are trying to solder a $1.50 socket instead of a $26 ram chip if you mess up the soldering.

edit: here is one source:

https://www.halted.com/ccp19762-ic-skt-40-pin-soj-socket-surface-mt-soj-40-cc-t-17631.htm

Peter