Dumb Question on SMT Interchangability...

[Len Lekx]

Probably a newbie question, but I'm going to ask anyway...

I've etched a circuit board with a few SMT components on it. I laid
it out for 1206-sized parts, but it's starting to seem that the only
parts I can get with the values I require are 0805-sized.

Hence my question - can I still solder 0805 components onto pads laid
out for 1206 components...? Comparing the pad spacing side-by-side on
my CAD program, it looks marginally possible.

 

[Rich Webb]

On Sun, 13 Mar 2011 12:09:02 -0400, Len Lekx <LFLekx@NOSPAM.rogers.com>
wrote:

Probably a newbie question, but I'm going to ask anyway...

I've etched a circuit board with a few SMT components on it. I laid
it out for 1206-sized parts, but it's starting to seem that the only
parts I can get with the values I require are 0805-sized.

Hence my question - can I still solder 0805 components onto pads laid
out for 1206 components...? Comparing the pad spacing side-by-side on
my CAD program, it looks marginally possible.

For one-off, home-brew prototyping, sure. If it fits, it fits. Of
course, it's not the pad spacing between 0805 and 1206 that matters,
it's the 1206 pad versus the 0805 component.

--
Rich Webb Norfolk, VA

 

[Phil Hobbs]

Rich Webb wrote:

On Sun, 13 Mar 2011 12:09:02 -0400, Len Lekx<LFLekx@NOSPAM.rogers.com
wrote:

Probably a newbie question, but I'm going to ask anyway...

I've etched a circuit board with a few SMT components on it. I laid
it out for 1206-sized parts, but it's starting to seem that the only
parts I can get with the values I require are 0805-sized.

Hence my question - can I still solder 0805 components onto pads laid
out for 1206 components...? Comparing the pad spacing side-by-side on
my CAD program, it looks marginally possible.

For one-off, home-brew prototyping, sure. If it fits, it fits. Of
course, it's not the pad spacing between 0805 and 1206 that matters,
it's the 1206 pad versus the 0805 component.

Yup. A 1206 pad is probably big enough that you can solder both ends of
an 0805 to one of them.

In a pinch, you can put 0805s on 0603 pads by standing them up like
billboards and turning them so they're diagonal to the pads. Not the
most robust solution, but a man's gotta do what a man's gotta do.

One of my customer's demos to their customer was saved by an ace
technician who managed to fit 0805 MF resistors onto 0402 pads that way.
Fortunately there was a nicely machined, black anodized aluminum
housing to hide that atrocity.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net

 

[Len Lekx]

On Sun, 13 Mar 2011 12:43:28 -0400, Rich Webb
<bbew.ar@mapson.nozirev.ten> wrote:

Hence my question - can I still solder 0805 components onto pads laid
out for 1206 components...? Comparing the pad spacing side-by-side on
my CAD program, it looks marginally possible.
For one-off, home-brew prototyping, sure. If it fits, it fits. Of
course, it's not the pad spacing between 0805 and 1206 that matters,
it's the 1206 pad versus the 0805 component.

True enough. The terminals have to be able to sit on the pads.

After some searching, though, I found that there ARE 1206-sized
capacitors in the values I'm looking for. It just seems a little
excessive to me, to use a part rated for 50VDC in a 5V circuit.

 

[Grant]

On Sun, 20 Mar 2011 09:59:00 -0400, Len Lekx <LFLekx@NOSPAM.rogers.com> wrote:

On Sun, 13 Mar 2011 12:43:28 -0400, Rich Webb
bbew.ar@mapson.nozirev.ten> wrote:

Hence my question - can I still solder 0805 components onto pads laid
out for 1206 components...? Comparing the pad spacing side-by-side on
my CAD program, it looks marginally possible.
For one-off, home-brew prototyping, sure. If it fits, it fits. Of
course, it's not the pad spacing between 0805 and 1206 that matters,
it's the 1206 pad versus the 0805 component.

True enough. The terminals have to be able to sit on the pads.

After some searching, though, I found that there ARE 1206-sized
capacitors in the values I'm looking for. It just seems a little
excessive to me, to use a part rated for 50VDC in a 5V circuit.

Whereas that seems perfectly normal to me

Grant.

 

[Michael A. Terrell]

Len Lekx wrote:

On Sun, 13 Mar 2011 12:43:28 -0400, Rich Webb
bbew.ar@mapson.nozirev.ten> wrote:

Hence my question - can I still solder 0805 components onto pads laid
out for 1206 components...? Comparing the pad spacing side-by-side on
my CAD program, it looks marginally possible.
For one-off, home-brew prototyping, sure. If it fits, it fits. Of
course, it's not the pad spacing between 0805 and 1206 that matters,
it's the 1206 pad versus the 0805 component.

True enough. The terminals have to be able to sit on the pads.

After some searching, though, I found that there ARE 1206-sized
capacitors in the values I'm looking for. It just seems a little
excessive to me, to use a part rated for 50VDC in a 5V circuit.

Why? Some people prefer to use 150 or 500 volt.


--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.

 

[Len Lekx]

On Sun, 20 Mar 2011 13:09:15 -0400, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

After some searching, though, I found that there ARE 1206-sized
capacitors in the values I'm looking for. It just seems a little
excessive to me, to use a part rated for 50VDC in a 5V circuit.
Why? Some people prefer to use 150 or 500 volt.

No particular reason... I'm so used to seeing 5V circuits that use
16V capacitors, it just seems like it's an unnecessarily large margin
- a crystal-oscillator circuit isn't likely to have 50-volt spikes.
(Is it...?)

 

[Michael A. Terrell]

Len Lekx wrote:

On Sun, 20 Mar 2011 13:09:15 -0400, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:

After some searching, though, I found that there ARE 1206-sized
capacitors in the values I'm looking for. It just seems a little
excessive to me, to use a part rated for 50VDC in a 5V circuit.
Why? Some people prefer to use 150 or 500 volt.

No particular reason... I'm so used to seeing 5V circuits that use
16V capacitors, it just seems like it's an unnecessarily large margin
- a crystal-oscillator circuit isn't likely to have 50-volt spikes.
(Is it...?)

That's not the point. You want some margin for noise or spikes in
the circuit, if you want it to keep working. If you run it right at the
edge, the failure rate goes up.


--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.