Embarrassingly basic PCB layout question: TO5-8 overlaid with DIP-8 okay?

[soapfoot]

I'm entirely self-taught so please forgive the super basic question.

If I wanted to be able to accommodate both a TO5-8 footprint and DIP-8 footprint, is this an okay strategy?



For all I know this is a super common thing to do--I've seen it done with through-hole DIP-8 and smaller SMT packages, but I can't recall ever having seen it done with DIP-8 and TO5-8. The only question is whether some of the pads might end up borderline too-close. Otherwise it seems it could work okay.

Any reason I shouldn't do this?

Thanks so much

 

[Lampie519]

If everything is done according your design rules (inductance and capacitance between the pins etc.) it should be ok.

 

[soapfoot]

These are just old-fashioned LM741 op amps operating at audio frequencies, nothing too critical.

 

[Brian Roth]

The clearances need to be "approved" by the company actually making the PC board.

Bri

 

[Brian Roth]

One other comment....in the posted layout, I see a few traces that intersect the corresponding "donuts" at an odd angle. Traces should go "center to center" of the corresponding donuts to reduce fabrication problems.

Bri

 

[soapfoot]

Thank you. This was just a super quick mockup for proof-of-concept

 

[Brian Roth]

Thank you. This was just a super quick mockup for proof-of-concept

I totally understand!

I guess that snapshot was from Kicad? shrug....looks like it to me.

I seldom do PCB layouts anymore, but Kicad is what I use.

In Kicad,you can set "Design Rules" which establish spacings for things like traces and how close to the edge, etc. The PCB manufacturer has corresponding rules. See what the PC board fab says for their standards and then add "a mil or two" on the layout.

I ASSume you already corresponded the pin differences between DIP9 and TO5-8. That always seems to confused me! lol

I expect Midnight Arrakis will chime in here with a long reply and I'll bow out <g>.

Bri

 

[Brian Roth]

I totally understand!

I guess that snapshot was from Kicad? shrug....looks like it to me.

I seldom do PCB layouts anymore, but Kicad is what I use.

In Kicad,you can set "Design Rules" which establish spacings for things like traces and how close to the edge, etc. The PCB manufacturer has corresponding rules. See what the PC board fab says for their standards and then add "a mil or two" on the layout.

I ASSume you already corresponded the pin differences between DIP8 and TO5-8. That always seems to confused me! lol

I expect Midnight Arrakis will chime in here with a long reply and I'll bow out <g>.

Bri

 

[Newmarket]

The design rules in whatever ECAD system bring used should warn you if there's a problem.
What you posted is all good just from looking at it.
Good idea. I often do this with SMT and Thru Hole. Or with cap footprints etc .

 

[soapfoot]

Thanks! I’m using EasyEDA

I’m probably way less experienced with this kind of thing than the average user here

 

[dmp]

I've been using EasyADA also - I got some PCBs last month that were really nice quality.
Under the file menu Design->Design Rule... you can set the clearance rule. Then it will alert you if the pin pads are too close together.
I would say pins 2 to 3 (inverting to non-inverting) and 6 to 7 (output to V+) are the ones to worry about, as they lie close together due to the rotation. I'm not sure what the minimum acceptable clearance is for those pins. If you had at least 0.1mm you'll probably be OK.
But you could rotate the TO5 footprint about 20deg CCW so those pins are practically touching to make it a non-issue.
There is a way in Easy ADA to save your own footprint for a part and then you could make this a single footprint part with the TO5 rotated and not have to track it in the PCB as two parts.

 

[soapfoot]

Current clearance is about .16 mm to the solder mask and about .25mm between the pads themselves. I’ll investigate the design rules, and the 20 degree rotation is a great idea!

 

[dmp]

Happy to help if you have more questions on easyADA - I've figured quite a bit out - but it's a pretty difficult software imo (but the price is right).
I got an order last month and the quality of the PCBs was excellent.

 

[KA-Electonics.com]

Maybe we should have a layout thread to share footprints and circuit fragments.

The OP looks fine to me though I agree with Bri regarding the trace hitting the center of the pad.

 

[dmp]

Maybe we should have a layout thread to share footprints and circuit fragments.

I think you can share between email addresses (as observer or editor) OR make the project public, but that would share with the whole world.
I'm currently struggling with a layout for a monitor controller - trying to reduce the number of vias, keep balanced traces together, etc...
I wish I knew the best way to approach it - a good organization of the parts in the PCB seems important before routing.
I would buy yours KA-elec, as it is perfect for what I want in many ways - except I want 3in, 5 out, and a few other features (talkback mute, foldback control, headphone out, etc...)

 

[soapfoot]

Okay! Rotating about 25 degrees gets me this, which seems much better.

Obviously it does not pass the design rule spec for pad clearance now (they're literally overlapping), but that should be fine, right?

 

[dmp]

I don't know if you can get them made like that. If they could make them it it would be fine.
But in the footprints you are telling it to have the plating and solder mask in ways that might conflict

 

[dmp]

A better way to do it might be to make a combined footprint for the opamp that has both footprints, connected in the footprint. I just tried this quickly and the attached image is what it looks like.

If you want to try this, click on the DIP part in your schematic, then open the footprint manager from the tools menu.
Search for your part's original footprint on the right side, then click on it. A green edit button will appear.
When you click edit, it will open the footprint in a new window, which you can now edit. You can move and create pads and create tracks. I added 8 pads in the circle and create tracks between them and the DIP pads. I turned off the solder mask on the right two pads by left clicking and going into the pad properties and making the 'solder mask expansion' = 0
I'm not sure if this should be zero or not - probably have to research that a bit.
After you finish making the footprint, save it into your workspace.
Then you can assign the footprint to parts in your schematic through the footprint manager.

 

[dmp]

I think you want to renumber the pads to match like this and then make sure they are connected correctly back in the footprint manager.

 

[KA-Electonics.com]

I think you can share between email addresses (as observer or editor) OR make the project public, but that would share with the whole world.
I'm currently struggling with a layout for a monitor controller - trying to reduce the number of vias, keep balanced traces together, etc...
I wish I knew the best way to approach it - a good organization of the parts in the PCB seems important before routing.
I would buy yours KA-elec, as it is perfect for what I want in many ways - except I want 3in, 5 out, and a few other features (talkback mute, foldback control, headphone out, etc...)

I use ExpressPCB and could either share images or .pcb files. In many cases an image of a fragment would be enough.

Thanks for considering the Monitor Controller. My area of interest is the mastering chain so I didn't include talkback functionality and ran out of real estate anyway. FWIW Markus' Insert Switchers that I sell can be used "in reverse" to make a 1 of 3 input selector using the backbone input and returns 1 & 2.