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'[EE] Generic SMD pad layout catalogue?'
2010\07\25@102009 by Peter

picon face
Is there such a catalogue? A few years ago major manufacturers added the
preferred pad dimensions to the datasheets of parts, including for passives like
resistors and capacitors. Plucking this data out of datasheets is very tedious
when verifying board layouts or when figuring out extreme space constraint
what-ifs. Surely there must be some catalogue of footprints? I was unable to
find such a thing. By catalogue, I mean some form of electronic document showing
the pads and dimensions, not necessarily EDIF files and especially not pad
artwork stored in proprietary layout tools. I know how to find those and it's
tedious but trivial to print out a proof sheet of those. Basically I'd like to
have proof sheets of pad layouts so I can pick and mix in what-if scenarios and
to prepare boards for readiness to take several types of parts to be changed
later (at place time).

-- Peter

2010\07\25@110429 by mcd

flavicon
face
> Surely there must be some catalogue of footprints? I was unable
> to find such a thing. By catalogue, I mean some form of electronic
> document showing the pads and dimensions, not necessarily EDIF
> files and especially not pad artwork stored in proprietary layout
> tools.

The gEDA suite includes the various pad layouts and rather than some
arcane format, as a FOSS tool, the formats are open, and happen to be
text, so with a little scripting you could have them in any form you want.
heck, you wouldn't even need to actually install the tools, just look at
the files.  Yeah, they aren't real pretty, basically lists of the pad
coordinates, but that is what you need.  Tedious, maybe, but not as
tedious as, say, some PDF document where you would have to re-type
everything.

--McD

2010\07\26@061148 by alan.b.pearce

face picon face
> Is there such a catalogue? A few years ago major manufacturers added
the
> preferred pad dimensions to the datasheets of parts, including for
passives like
> resistors and capacitors. Plucking this data out of datasheets is very
tedious
> when verifying board layouts or when figuring out extreme space
constraint
> what-ifs. Surely there must be some catalogue of footprints? I was
unable to
> find such a thing. By catalogue, I mean some form of electronic
document showing
> the pads and dimensions, not necessarily EDIF files and especially not
pad
> artwork stored in proprietary layout tools. I know how to find those
and it's
> tedious but trivial to print out a proof sheet of those. Basically I'd
like to
> have proof sheets of pad layouts so I can pick and mix in what-if
scenarios and
> to prepare boards for readiness to take several types of parts to be
changed
> later (at place time).

Yes, it is known as JEDEC. The biggest problem is identifying the JEDEC
case from the chip manufacturers drawing, as not many manufacturers put
the JEDEC designation on their drawing. See
http://www.jedec.org/standards-documents and you may have to register to
download the documents, but I believe it is not too onerous.
-- Scanned by iCritical.

2010\07\29@055216 by Peter

picon face
<alan.b.pearce <at> stfc.ac.uk> writes:
> Yes, it is known as JEDEC. The biggest problem is identifying the JEDEC
....

If it would have been so simple I would have considered that. I am not looking
for the package dimensions, but for the solder pad dimensions and shapes. The
latter are more a manufacturer recommendation than a JEDEC standard, or so it
seems.

thanks,

-- Peter


2010\07\29@060932 by Djula Djarmati

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On 29-Jul-10 11:52, Peter wrote:
> <alan.b.pearce<at>  stfc.ac.uk>  writes:
>> Yes, it is known as JEDEC. The biggest problem is identifying the JEDEC
> ...
>
> If it would have been so simple I would have considered that. I am not looking
> for the package dimensions, but for the solder pad dimensions and shapes. The
> latter are more a manufacturer recommendation than a JEDEC standard, or so it
> seems.
>
> thanks,
>
> -- Peter

Peter,

Try LP Viewer, it's a free (registration required) viewer+database with three types of pads: large (for hand soldering), medium and minimal.

We've had very good luck soldering these pads.

<http://www.mentor.com/products/pcb-system-design/library-tools/lp-wizard/lp-viewer-download>

Djul

2010\07\29@061812 by alan.b.pearce

face picon face
> > Yes, it is known as JEDEC. The biggest problem is identifying the
JEDEC
> ...
>
> If it would have been so simple I would have considered that. I am not
looking
> for the package dimensions, but for the solder pad dimensions and
shapes. The
> latter are more a manufacturer recommendation than a JEDEC standard,
or so it
> seems.
>
> thanks,
>
> -- Peter

One of the problems you face is that there are often two recommended pad
layouts, depending on if you are reflow soldering or not. IIRC reflow
soldering tends to use smaller pads.
-- Scanned by iCritical.

2010\07\29@075726 by Olin Lathrop

face picon face
Peter wrote:
> If it would have been so simple I would have considered that. I am
> not looking for the package dimensions, but for the solder pad
> dimensions and shapes.

Which require knowing the package dimensions to derive.

I don't understand the problem.  Every datasheet has detailed package
dimensions.  Workable footprints can be decided from those easily enough.  I
thought your issues was that you wanted to know the mechanical range of the
generic package type instead of a small sampling of particular manufacturer
implementations.  That part makes sense, although in practise a SO14 is
pretty much a SO14, a SOT23 a SOT23, etc.  Once you have the generic
definition, you should be all set and be able to define a footprint that
works for the full mechanical tollerance range.

There is no such thing as "standard" footprints, only standard packages.
Most manufacturer suggested footprints suck anyway.  They usually only take
into account how to hook up to their part, but of course they don't know
about other constraints on your board, how it will be assembled, and debug
issues you may want to build in.  Manufacturer footprints are basically
suggestions for the lazy or incompetent, and I've seen some outright bad
ones.  Personally I never even look at the suggested footprints, since the
manufacturer doesn't know what I want.  Look at the mechanical specs
carefully, noting all the worst case tollerances, and make your own
footprint.  This really isn't a problem.

2010\07\29@091640 by PICdude

flavicon
face
Quoting spam_OUTalan.b.pearceTakeThisOuTspamstfc.ac.uk:

> One of the problems you face is that there are often two recommended pad
> layouts, depending on if you are reflow soldering or not. IIRC reflow
> soldering tends to use smaller pads.


And as I understand it (from discussions at the last SMTA event I went  to) that the pad sizes will vary based on the height of the part (to  vary the quantity of solder-paste applied), so two different  0805-footprint parts may require different pad dimensions.  So far,  I've had great success following the manufacturer's recommended  layouts in the datasheets.  I've so far not had to change the pad  dimensions for hand soldering, but I've made pads larger if they're  supporting a component that is expected to get hot.

Cheers,
-Neil.

2010\07\29@093453 by alan.b.pearce

face picon face
> And as I understand it (from discussions at the last SMTA event I went
> to) that the pad sizes will vary based on the height of the part (to
> vary the quantity of solder-paste applied), so two different
> 0805-footprint parts may require different pad dimensions.  So far,
> I've had great success following the manufacturer's recommended
> layouts in the datasheets.  I've so far not had to change the pad
> dimensions for hand soldering, but I've made pads larger if they're
> supporting a component that is expected to get hot.
>
> Cheers,
> -Neil.

Yes, that is because a 'good' joint has the solder fillet come half way
up the component metallization. So a thin component requires a lower
fillet, but the only way to get sufficient fillet on a taller component
is to have a larger pad.
-- Scanned by iCritical.

2010\07\29@121828 by Jon Chandler

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face
On Thu, Jul 29, 2010 at 4:57 AM, Olin Lathrop <.....olin_piclistKILLspamspam@spam@embedinc.com>wrote:

>
> I don't understand the problem.  Every datasheet has detailed package
> dimensions.  Workable footprints can be decided from those easily enough....
>
>


> Most manufacturer suggested footprints suck anyway.
>


Is it just me or do Olin's comments add up to less than zero

2010\07\29@123506 by alan.b.pearce

face picon face


> -----Original Message-----
> From: piclist-bouncesspamKILLspammit.edu [.....piclist-bouncesKILLspamspam.....mit.edu] On
Behalf Of Jon
> Chandler
> Sent: 29 July 2010 17:17
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Generic SMD pad layout catalogue?
>
> On Thu, Jul 29, 2010 at 4:57 AM, Olin Lathrop
<EraseMEolin_piclistspam_OUTspamTakeThisOuTembedinc.com>wrote:
>
> >
> > I don't understand the problem.  Every datasheet has detailed
package
> > dimensions.  Workable footprints can be decided from those easily
enough...
> >
> >
>
>
> > Most manufacturer suggested footprints suck anyway.
> >
>
>
> Is it just me or do Olin's comments add up to less than zero?

Well, I find him partly correct on this one. Often the manufacturers
don't have enough length on the outside end of the pad for hand
soldering, and sometimes when you work through the dimensional
tolerances the inside to inside spacing to too far to get a proper
fillet at the back of the leg.

We have found that it does not pay to take the manufacturers data at
face value, but to at least double check it. We now have a spreadsheet
for calculating such things easily.
-- Scanned by iCritical.

2010\07\29@141512 by Olin Lathrop

face picon face
Jon Chandler wrote:
> Is it just me or do Olin's comments add up to less than zero?

No, it's just you.

I'm working on a PIC controlled gizmo for sucking information from your
brain, but every time I try to test it I forget what it's supposed to do.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000

2010\07\29@164332 by Robert Young

picon face


> From: olin_piclistspamspam_OUTembedinc.com
> To: @spam@piclistKILLspamspammit.edu
> Subject: Re: [EE] Generic SMD pad layout catalogue?
> Date: Thu, 29 Jul 2010 14:15:29 -0400
>
> Jon Chandler wrote:
> > Is it just me or do Olin's comments add up to less than zero?
>
> No, it's just you.
>
> I'm working on a PIC controlled gizmo for sucking information from your
> brain, but every time I try to test it I forget what it's supposed to do.
>
Olin's comment to pull the pad sizes from the component data sheet is on the money.  Pad sizes are a function of the part foot print AND it soldering qualities.  
Olin, please turn off your gizmo.  I think you have the wrong base address programmed because I keep screwing up the stuff I'm doing today.

Rob
                                         

2010\07\29@170639 by Vitaliy

face
flavicon
face
alan.b.pearce@stfc.ac.uk wrote:
> Well, I find him partly correct on this one. Often the manufacturers
> don't have enough length on the outside end of the pad for hand
> soldering, and sometimes when you work through the dimensional
> tolerances the inside to inside spacing to too far to get a proper
> fillet at the back of the leg.
>
> We have found that it does not pay to take the manufacturers data at
> face value, but to at least double check it.

FWIW, we came to the same conclusion. We had to modify several packages based on our CM's suggestions, or our own observations.

We use EAGLE's "description" field to record the datasheet that the package is based on, and the change log (who, when, what, why).


> We now have a spreadsheet
> for calculating such things easily.

Is this something you're willing to share? :)

Vitaliy

2010\07\29@230715 by RussellMc

face picon face
> every time I try to test it I forget what it's supposed to do.

What what's supposed to do?

     RM

What what's supposed to do?

     RM

What what's supposed to do?

     RM

What what's supposed to do?

     RM

What ...


 *** Error: Message too large. Truncated. **

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