Homebrew PCBs

What is the minimum pad size (in mils) for home made PC boards?  (Single
Sided).

Thanks,
Chris Maness


[Non-text portions of this message have been removed]

--- In Homebrew_PCBs@yahoogroups.com, Chris Maness <chris@...> wrote:
>
> What is the minimum pad size (in mils) for home made PC boards?  (Single
> Sided).
> 
> Thanks,
> Chris Maness
> 
> 


That's like asking how long is a piece of string. The minimum size depends on far too many factors, what method are you using to make your boards, and what sort of pads?

On 05/04/2010 21:36, Chris Maness wrote:
> What is the minimum pad size (in mils) for home made PC boards?  (Single
> Sided).

It depends on your technique.

Leon
-- 
Leon Heller
G1HSM

I am planning on using a positive photo resist board, and using a .8mm drill
bit.

Chris (a n00b)
KQ6UP

On Mon, Apr 5, 2010 at 1:53 PM, Leon Heller <leon355@...> wrote:

> On 05/04/2010 21:36, Chris Maness wrote:
> > What is the minimum pad size (in mils) for home made PC boards?  (Single
> > Sided).
>
> It depends on your technique.
>
> Leon
> --
> Leon Heller
> G1HSM
>
>
> ------------------------------------
>
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>
>


[Non-text portions of this message have been removed]

A standard requirement for pad sizes is a 5 mil annulus. This means there
must be .005" all around the hole (i.e. a 28 mil hole would require a 38 mil
pad). Something a little larger than this (maybe 10 mils) is recommended for
solderability.

On Mon, Apr 5, 2010 at 3:04 PM, Chris Maness <chris@chrismaness.com> wrote:

>
>
> I am planning on using a positive photo resist board, and using a .8mm
> drill
> bit.
>
> Chris (a n00b)
> KQ6UP
>
> On Mon, Apr 5, 2010 at 1:53 PM, Leon Heller <leon355@...<leon355%40btinternet.com>>
> wrote:
>
> > On 05/04/2010 21:36, Chris Maness wrote:
> > > What is the minimum pad size (in mils) for home made PC boards? (Single
> > > Sided).
> >
> > It depends on your technique.
> >
> > Leon
> > --
> > Leon Heller
> > G1HSM
> >
> >
> > ------------------------------------
> >
> > Be sure to visit the group home and check for new Links, Files, and
> Photos:
> > http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
> >
> >
> >
> >
>
> [Non-text portions of this message have been removed]
>
>  
>



-- 
Paul Mateer, AA9GG
Elan Engineering Corp.
www.elanengr.com
NAQCC 3123, SKCC 4628, FPQRP 2003


[Non-text portions of this message have been removed]

On 05/04/2010 22:04, Chris Maness wrote:
> I am planning on using a positive photo resist board, and using a .8mm drill
> bit.

It still depends on your technique and equipment.

Leon
-- 
Leon Heller
G1HSM

On Mon, 5 Apr 2010 13:36:43 -0700, you wrote:

>What is the minimum pad size (in mils) for home made PC boards?  (Single
>Sided).

Through hole parts, possibly .040 to .066, big parts (power diodes),
larger.  

Depending on the process, that "typical" value can be smaller.  IMHO,
toner transfer likes .010 traces, can tolerate 0.04 pads (with 0.023
vias), and so.

Properly exposed photoresist can tolerate less, say .008 traces.  Much
depends on the physical size of the part, hole it needs, and the
process you use.  Add in current needed and size of trace, and you go
from signal ratings (what I gave), to power ratings, much larger.

Harvey

>
>Thanks,
>Chris Maness
>
>
>[Non-text portions of this message have been removed]
>
>
>
>------------------------------------
>
>Be sure to visit the group home and check for new Links, Files, and Photos:
>http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>

As others have pointed out, it is dependant on many other factors.  If you are doing surface mount parts, the pad needs to be about 10 mils greater in width than the leg (rough number).

For through holes, I prefer a pad that is as big as I can make it.  Small rings are hard to solder and can easily lift off the backing.  I try not to get much smaller than a 15 mil ring.  So, if your hole is 50 mils, it would be 50 + 15 + 15 = 80 mills in diameter.  This is still a rough number but it works for me.

Small rings are hard to solder and provide very little surface area for the solder to exists. I have found that anything smaller than 10 mills in width often lead to troubles as mentioned above.

What can help is also to make the pads oval in shape, this provides for better copper to backer adhesion and easier soldering. But again, watch your sides (narrow width) so that you still have some material there after drilling.

Chris



--- In Homebrew_PCBs@yahoogroups.com, Chris Maness <chris@...> wrote:

>
> What is the minimum pad size (in mils) for home made PC boards?  (Single
> Sided).
> 
> Thanks,
> Chris Maness
> 
> 
> [Non-text portions of this message have been removed]
>

In my relatively limited experience, one of the key factors is how precisely you can drill. My most recent board has .045 diameter via pads, drilled with a .6mm drill (0.024"). Even though I managed to get the registration between the top and bottom more or less perfect as far as the toner transfer and etch, I discovered that it was easy to drill the holes at an angle, at least using HSS drill bits. The drill is so small that it bends very easily; you can be off-center just a bit; the bit goes in right (because of the little etched dimple created by my software), but it comes out in the wrong place.

Obviously, I need to work on my drilling, both equipment and technique!

--- In Homebrew_PCBs@yahoogroups.com, Chris Maness <chris@...> wrote:

>
> What is the minimum pad size (in mils) for home made PC boards?  (Single
> Sided).
> 
> Thanks,
> Chris Maness
> 
> 
> [Non-text portions of this message have been removed]
>

I think I am going to go with the big ol' fatty 80 mil pads.  Most of the
pads in my CAD program are already that size.  I just had to change a few.

Regards,
Chris Maness

On Mon, Apr 5, 2010 at 3:56 PM, awakephd <a_wake@...> wrote:

> In my relatively limited experience, one of the key factors is how
> precisely you can drill. My most recent board has .045 diameter via pads,
> drilled with a .6mm drill (0.024"). Even though I managed to get the
> registration between the top and bottom more or less perfect as far as the
> toner transfer and etch, I discovered that it was easy to drill the holes at
> an angle, at least using HSS drill bits. The drill is so small that it bends
> very easily; you can be off-center just a bit; the bit goes in right
> (because of the little etched dimple created by my software), but it comes
> out in the wrong place.
>
> Obviously, I need to work on my drilling, both equipment and technique!
>
> --- In Homebrew_PCBs@yahoogroups.com, Chris Maness <chris@...> wrote:
> >
> > What is the minimum pad size (in mils) for home made PC boards?  (Single
> > Sided).
> >
> > Thanks,
> > Chris Maness
> >
> >
> > [Non-text portions of this message have been removed]
> >
>
>
>
>
> ------------------------------------
>
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>
>


[Non-text portions of this message have been removed]

awakephd wrote:
> In my relatively limited experience, one of the key factors is how precisely you can drill. My most recent board has .045 diameter via pads, drilled with a .6mm drill (0.024"). Even though I managed to get the registration between the top and bottom more or less perfect as far as the toner transfer and etch, I discovered that it was easy to drill the holes at an angle, at least using HSS drill bits. The drill is so small that it bends very easily; you can be off-center just a bit; the bit goes in right (because of the little etched dimple created by my software), but it comes out in the wrong place.
>
> Obviously, I need to work on my drilling, both equipment and technique!
>
>   
The trick is to not try to drill the whole thing in one pass; the tip 
gets loaded and will wander off course.
Take a few 'pecks' with each only going 5-10 mils deeper while backing 
the bit completely out between
each peck and don't feed in too fast.

This is the technique used on NC machines to drill really fine (6 mil) 
holes through 60 mil boards.

Bruce

On Mon, 05 Apr 2010 22:56:10 -0000, you wrote:

>In my relatively limited experience, one of the key factors is how precisely you can drill. My most recent board has .045 diameter via pads, drilled with a .6mm drill (0.024"). Even though I managed to get the registration between the top and bottom more or less perfect as far as the toner transfer and etch, I discovered that it was easy to drill the holes at an angle, at least using HSS drill bits. The drill is so small that it bends very easily; you can be off-center just a bit; the bit goes in right (because of the little etched dimple created by my software), but it comes out in the wrong place.
>
>Obviously, I need to work on my drilling, both equipment and technique!

Carbide bits do not bend, they just break.  This is the first example
I have seen where this is an advantage.  High speed spindle is a very
good idea, 20K RPM and up is better.

Drill press only.

Harvey

>
>--- In Homebrew_PCBs@yahoogroups.com, Chris Maness <chris@...> wrote:
>>
>> What is the minimum pad size (in mils) for home made PC boards?  (Single
>> Sided).
>> 
>> Thanks,
>> Chris Maness
>> 
>> 
>> [Non-text portions of this message have been removed]
>>
>
>
>
>
>------------------------------------
>
>Be sure to visit the group home and check for new Links, Files, and Photos:
>http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>

On 05/04/2010 23:40, Chris wrote:
>
> As others have pointed out, it is dependant on many other factors.  If you are doing surface mount parts, the pad needs to be about 10 mils greater in width than the leg (rough number).
>
> For through holes, I prefer a pad that is as big as I can make it.  Small rings are hard to solder and can easily lift off the backing.  I try not to get much smaller than a 15 mil ring.  So, if your hole is 50 mils, it would be 50 + 15 + 15 = 80 mills in diameter.  This is still a rough number but it works for me.
>
> Small rings are hard to solder and provide very little surface area for the solder to exists. I have found that anything smaller than 10 mills in width often lead to troubles as mentioned above.
>
> What can help is also to make the pads oval in shape, this provides for better copper to backer adhesion and easier soldering. But again, watch your sides (narrow width) so that you still have some material there after drilling.
>


I often use teardrops.

Leon
-- 
Leon Heller
G1HSM

--- In Homebrew_PCBs@yahoogroups.com, Chris Maness <chris@...> wrote:
>
> What is the minimum pad size (in mils) for home made PC boards?  (Single
> Sided).
> 
> Thanks,
> Chris Maness
> 
> 
> [Non-text portions of this message have been removed]
>

I drill the holes first then laminate dry film resist. UV expose with a film negative, develop the image, etch and strip the photo resist. The copper pad is never stressed this way and very small annular rings are possible. The only problem will be the weak copper adhesion with such a small copper area. Any component movement and the copper bond will break. With all of that in mind, it's best to use a larger annular ring on single sided boards. Most of my designs are surface mount and single sided but any through holes are allowed at least .020" around the hole and more if possible.

>
> --- In Homebrew_PCBs@yahoogroups.com, Chris Maness <chris@...> wrote:
> >
> > What is the minimum pad size (in mils) for home made PC boards?  (Single
> > Sided).
> >
> > Thanks,
> > Chris Maness
> >
> >
> > [Non-text portions of this message have been removed]
> >
>
> I drill the holes first then laminate dry film resist. UV expose with a
> film negative, develop the image, etch and strip the photo resist. The
> copper pad is never stressed this way and very small annular rings are
> possible. The only problem will be the weak copper adhesion with such a
> small copper area. Any component movement and the copper bond will break.
> With all of that in mind, it's best to use a larger annular ring on single
> sided boards. Most of my designs are surface mount and single sided but any
> through holes are allowed at least .020" around the hole and more if
> possible.
>
>
I was able to adjust my lands in the CAD drawing.  They are all beefy now.
80mils, and the inner hole is 30mils.  These should be OK.  I will be
experimenting more later.

Chris


[Non-text portions of this message have been removed]

> > What is the minimum pad size (in mils) for home made PC boards?  

AT  www.Eurocircuits.com there are a guide , called design guidelines,
In this you can find many ideas on what is the normal practice for PCB layout .
alex

Thanks, I'll give that a try. My personal experience suggests more a matter of not getting the board really on center than of it wandering off while drilling, but perhaps it is a combination of the two. I know that my equipment could be improved -- I am using a drill press with only 3200 rpm top speed, and there is some runout in the spindle -- and I suspect switching to carbide drill bits would help, IF I used them with a better and faster spindle. The biggest surprise for me is that I am getting usable results, for the most part, in spite of not really having the right equipment on hand.

--- In Homebrew_PCBs@yahoogroups.com, Bruce Parham <obparham@...> wrote:

>
> awakephd wrote:
> > In my relatively limited experience, one of the key factors is how precisely you can drill. My most recent board has .045 diameter via pads, drilled with a .6mm drill (0.024"). Even though I managed to get the registration between the top and bottom more or less perfect as far as the toner transfer and etch, I discovered that it was easy to drill the holes at an angle, at least using HSS drill bits. The drill is so small that it bends very easily; you can be off-center just a bit; the bit goes in right (because of the little etched dimple created by my software), but it comes out in the wrong place.
> >
> > Obviously, I need to work on my drilling, both equipment and technique!
> >
> >   
> The trick is to not try to drill the whole thing in one pass; the tip 
> gets loaded and will wander off course.
> Take a few 'pecks' with each only going 5-10 mils deeper while backing 
> the bit completely out between
> each peck and don't feed in too fast.
> 
> This is the technique used on NC machines to drill really fine (6 mil) 
> holes through 60 mil boards.
> 
> Bruce
>

Absolutely agreed -- as I posted just now (before I read your post), I know that what I'm using is far from ideal. I have plans to make a high-speed spindle that I can use with my drill press, but haven't had time to work on that project yet -- so much to do, so little time ...

--- In Homebrew_PCBs@yahoogroups.com, Harvey White <madyn@...> wrote:

>
> High speed spindle is a very
> good idea, 20K RPM and up is better.
> 
> Drill press only.
> 
> Harvey

--- In Homebrew_PCBs@yahoogroups.com, "awakephd" <a_wake@...> wrote:
> two. I know that my equipment could be improved -- I am using a drill >press with only 3200 rpm top speed, and there is some runout in the >spindle -- and I suspect switching to carbide drill bits would help, >IF I used them with a better and faster spindle. The biggest 

That is the same I use - an el cheapo small drill press with visible runout (not much, but visible) on spindle at 3200 RPM.  I switched to carbide bits and they are SO MUCH better than the HSS bits. The carbide bits don't "walk" during drilling "as bad" as did the HSS.

I like BIG pads - without a solder mask to help hold the copper in place, it's easy for them to lift during rework. My usual pad size is as large as possible - on .010" pin spacing sometimes have a very small space between next pin. ON DIP sockets I will use a longer pad to have more copper left on board and still have room to run a trace between pads.

Ken H>

> >   
> The trick is to not try to drill the whole thing in one pass; the tip 
> gets loaded and will wander off course.
> Take a few 'pecks' with each only going 5-10 mils deeper while backing 
> the bit completely out between
> each peck and don't feed in too fast.
> 
> This is the technique used on NC machines to drill really fine (6 mil) 
> holes through 60 mil boards.
> 
> Bruce
>


I find I get the best results doing a quick jab, using a high speed carbide bit with a drill stand I built out of a little precision slide it works great. Take a moment to line it up carefully and then plunge, a carbide bit turning around 20KRPM plunges through the FR4 board like a hot knife through butter.

On 06/04/2010 22:46, James wrote:
>

>
> I find I get the best results doing a quick jab, using a high speed carbide bit with a drill stand I built out of a little precision slide it works great. Take a moment to line it up carefully and then plunge, a carbide bit turning around 20KRPM plunges through the FR4 board like a hot knife through butter.

High-speed is best with tungsten carbide drills. My drill only does 
18,000 rpm.

Leon
-- 
Leon Heller
G1HSM

--- In Homebrew_PCBs@yahoogroups.com, Leon Heller <leon355@...> wrote:
>
> On 06/04/2010 22:46, James wrote:
> >
> 
> >
> > I find I get the best results doing a quick jab, using a high speed carbide bit with a drill stand I built out of a little precision slide it works great. Take a moment to line it up carefully and then plunge, a carbide bit turning around 20KRPM plunges through the FR4 board like a hot knife through butter.
> 
> High-speed is best with tungsten carbide drills. My drill only does 
> 18,000 rpm.
> 
> Leon
> -- 
> Leon Heller
> G1HSM
>


I don't actually know the RPM of my drill, I used a nice Maxon precision DC motor which is rated 11K RPM under load at 24V, and I run it around 32V with very light load, it's nice and smooth and turns fast. Whatever the case, it drills a nice hole with carbide bits, and the only one I've broken since building this is a 0.020" when my finger twitched while I was holding down the PCB.

On 04/09/2010 01:01 PM, James wrote:

> I don't actually know the RPM of my drill, I used a nice Maxon
> precision DC motor which is rated 11K RPM under load at 24V, and I
> run it around 32V with very light load, it's nice and smooth and
> turns fast. Whatever the case, it drills a nice hole with carbide
> bits, and the only one I've broken since building this is a 0.020"
> when my finger twitched while I was holding down the PCB.

You know, I am pretty satisfied with:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94606

I use those cheap, "regular" bits with a battery black&decker drill. 
Granted, I try to do SMD as much as possible, so I do not normally have 
many holes to do... but the fact that I can start "slow" with the drill 
eases the accuracy of the hole and, as those bits are relatively 
"elastic" I've never broke one. So far the bits hold sharpness decently.

bye
as

That's also what I have been using. I am not dissatisfied with them; just not completely satisfied with my technique! :)

One of these days I'd like to work up a CNC drill ...

--- In Homebrew_PCBs@yahoogroups.com, Alessio Sangalli <alesan@...> wrote:

>
> On 04/09/2010 01:01 PM, James wrote:
> 
> > I don't actually know the RPM of my drill, I used a nice Maxon
> > precision DC motor which is rated 11K RPM under load at 24V, and I
> > run it around 32V with very light load, it's nice and smooth and
> > turns fast. Whatever the case, it drills a nice hole with carbide
> > bits, and the only one I've broken since building this is a 0.020"
> > when my finger twitched while I was holding down the PCB.
> 
> You know, I am pretty satisfied with:
> http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94606
> 
> I use those cheap, "regular" bits with a battery black&decker drill. 
> Granted, I try to do SMD as much as possible, so I do not normally have 
> many holes to do... but the fact that I can start "slow" with the drill 
> eases the accuracy of the hole and, as those bits are relatively 
> "elastic" I've never broke one. So far the bits hold sharpness decently.
> 
> bye
> as
>