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PCB schematic design issues #gettingstarted

 

Hello, I'm new to using this software and pretty much everything that has to do with PCB design and manufacturing products. I'm currently trying to design and build a flashing LED circuit for an engineering project. The issue I'm inquiring about has to do with the closeness of the THT pads for my two transistors. When I printed out the trace on a piece of paper from a PDF format, the pads are extremely close together and my engineering teacher is concerned that this will hinder the traces and will make it very difficult to produce a working circuit. There is an attached screen shot of the PDF.

Screenshot _17_.png

 

If you used a predefined footprint for the transistors (from the KiCAD footprint libraries that are part of the full installation) you should have no problems. I too have noticed the closeness of the pads, but they are useable even for hand-soldered assembly. If you wish, you can change the footprint to another where the pads are larger and/or farther apart (i.e. TO-92_Inline_Wide).

Capture.PNG

 

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Hello,
??? Welcome to the group.
- Can you specify where the pads are too close together? If it's at the level of the footprint of the transistors, you have to choose another one or create one specific to your needs (it's very easy with a little practice).
- Why do you use such thin cooper? And no ground plane ?
??? Regards,
??? Jean-Paul

****
Jean-Paul Gendner
03 88 27 03 44
Site :


Le 2022-02-16 à 19:32, sean.buchinger@... a écrit?:

Hello, I'm new to using this software and pretty much everything that has to do with PCB design and manufacturing products. I'm currently trying to design and build a flashing LED circuit for an engineering project. The issue I'm inquiring about has to do with the closeness of the THT pads for my two transistors. When I printed out the trace on a piece of paper from a PDF format, the pads are extremely close together and my engineering teacher is concerned that this will hinder the traces and will make it very difficult to produce a working circuit. There is an attached screen shot of the PDF.

 

Hi Sean, welcome!

Yes those pads are close, and will be difficult to solder by hand.

Have a look in the footprint list, and for quite a few footprints you
will usually find two versions, one as you have found and another marked
something like

TO92L_Handsolder.kicad.mod

As the name implies these are a lot easier to solder, there is a bit mor
spacing between the pins which also give the solder resist a chance to
get in.

Andy




On Wed, 16 Feb 2022 10:32:57 -0800
sean.buchinger@... wrote:

Hello, I'm new to using this software and pretty much everything that has to do with PCB design and manufacturing products. I'm currently trying to design and build a flashing LED circuit for an engineering project. The issue I'm inquiring about has to do with the closeness of the THT pads for my two transistors. When I printed out the trace on a piece of paper from a PDF format, the pads are extremely close together and my engineering teacher is concerned that this will hinder the traces and will make it very difficult to produce a working circuit. There is an attached screen shot of the PDF.
 

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All, ??

I have used ?TO-92 for a ? transistor ?footprint ?several times with no problems…. ? at ?frequencies below ?5 Mhz.

Stephen

On Feb 16, 2022, at 4:53 PM, Andy <andygio@...> wrote:

Hi Sean, welcome!

Yes those pads are close, and will be difficult to solder by hand.

Have a look in the footprint list, and for quite a few footprints you
will usually find two versions, one as you have found and another marked
something like

TO92L_Handsolder.kicad.mod

As the name implies these are a lot easier to solder, there is a bit mor
spacing between the pins which also give the solder resist a chance to
get in.

Andy




On Wed, 16 Feb 2022 10:32:57 -0800
sean.buchinger@...?wrote:

Hello, I'm new to using this software and pretty much everything that has to do with PCB design and manufacturing products. I'm currently trying to design and build a flashing LED circuit for an engineering project. The issue I'm inquiring about has to do with the closeness of the THT pads for my two transistors. When I printed out the trace on a piece of paper from a PDF format, the pads are extremely close together and my engineering teacher is concerned that this will hinder the traces and will make it very difficult to produce a working circuit. There is an attached screen shot of the PDF.
 

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The normal way to allow enough space between tht transistor terminals, unless you have a *very* high tech PCB fabrication system, is to offset the middle (usually base) connection vertically. I would suggest the TO-92L_Wide footprint if you are going to etch your own PCB. If so, then it would also be advisable to edit the footprint for your PCB (and save it in a new library for future use), so that there is a little more copper around the holes. That will make hand-drilling less likely to destroy the pad.

Also, double check that the numbering of the transistor terminals on the schematic symbol matches the data sheet and footprint, because a few TO92 transistors have the collector in the middle.

hth

Andrew

On 16/02/2022 18:32, sean.buchinger@... wrote:
Hello, I'm new to using this software and pretty much everything that has to do with PCB design and manufacturing products. I'm currently trying to design and build a flashing LED circuit for an engineering project. The issue I'm inquiring about has to do with the closeness of the THT pads for my two transistors. When I printed out the trace on a piece of paper from a PDF format, the pads are extremely close together and my engineering teacher is concerned that this will hinder the traces and will make it very difficult to produce a working circuit. There is an attached screen shot of the PDF. 
-- 
e: andrew@...

 

Having a look to the supposed to be the two TO-92 (package with Transistor EBC pins in-line)
in there on your PCB (extracted from your png file):
image.png

Have a look to KiCad's 'footprint library':
image.png
You shall then see this (by searching for TO92 possibilities, so as to select the 'best one which could fit your need'):

image.png

For? TO92 '3 pins in-line' (double-clicking on the different items in the list to show the pads footprints):
image.png? probably the one you are using (and normally with no difficulty to solder...)

or
could select a 'larger footprint one' (if you still worry about the one you are using):
?image.png image.png (both of these footprints having the 'same pitch'...)


You could also use the following one (which could be better if you are 'not confortable in soldering')
but for TO92 package 'with not in-line pins'.
If you have already procured your TO92's with in-line pins, to bend the pins before being able to insert the parts and then solder each of these pins...

image.png

With hope it will help (or answer your coach's fears, if any ?).

KR
GerardFX





Le?jeu. 17 févr. 2022 à?17:26, Andrew Armstrong <andrew@...> a écrit?:

The normal way to allow enough space between tht transistor terminals, unless you have a *very* high tech PCB fabrication system, is to offset the middle (usually base) connection vertically. I would suggest the TO-92L_Wide footprint if you are going to etch your own PCB. If so, then it would also be advisable to edit the footprint for your PCB (and save it in a new library for future use), so that there is a little more copper around the holes. That will make hand-drilling less likely to destroy the pad.

Also, double check that the numbering of the transistor terminals on the schematic symbol matches the data sheet and footprint, because a few TO92 transistors have the collector in the middle.

hth

Andrew

On 16/02/2022 18:32, sean.buchinger@... wrote:
Hello, I'm new to using this software and pretty much everything that has to do with PCB design and manufacturing products. I'm currently trying to design and build a flashing LED circuit for an engineering project. The issue I'm inquiring about has to do with the closeness of the THT pads for my two transistors. When I printed out the trace on a piece of paper from a PDF format, the pads are extremely close together and my engineering teacher is concerned that this will hinder the traces and will make it very difficult to produce a working circuit. There is an attached screen shot of the PDF. 
-- 
e: andrew@...

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