Where To Get Miniaturized Footprints for SMD Components (Resistors, ICs, Transistors etc.)

[Hi-Q]

Hey,

For most of the SMD components we use, the manufacturers provide recommended footprints (pad layout geometry).

I assume they were designed to offer optimum soldering results with a high margin with various surface finishings on components and PCB, a wide variety of processes like convection heating, infrared heating, soldering in air, nitrogen, using vapor phase soldering and so on.

Sometimes there are situations where PCB space is extremely scarce and in order to fit all the required components onto the PCB it is necessary to sacrifice some of the above mentioned margin.
I believe that many of us at least sometimes have that problem and so I wonder if someone knows how the pads for certain SMD components can be miniaturized without running into too many problems with the reflow soldering.

As an example, I have an 0805 pad layout with the pads being 44 mil long and 50 mil wide whth a center to center spacing of 80 mil (free space between pads 36 mil, overall length 124 mil).
Then I needed a shorter footprint to fit a 0805 resistor into a gap between other components but at the same time allowing to route three tracks under the resistor with a 6mil technology (but 7 mil pad to track spacing because of the solder mask).
In order to be able to place the resistor I needed to make the pads shorter (32 mil) and the center to center spacing to 76 mil (free space between pads 44 mil, overall length 108 mil).

This one is not yet tested, but if the resistor is actually required and populated I can report on the results.

Now I am curious if some of you have tested miniaturized footprints and can give me hints on working geometries.
I'd be especially interested in 0805, 0603 and 0402 footprints and shrinked SO packages like SSOP, TSSOP, VSSOP, MSOP, µMax, SC70-5 and SC70-6 and similar packages.

Regards,
Hi-Q
P.S.:
I know that one can use smaller components if space is scarce, but not all components are available in the packages we'd wish for.

 

[Carry for cents bazar]

The footprints can be found at:
snapeda.com

You can always create the footprints by yourself. Google footprint SSOP exact dimensions or measure it with a ruler.

If you buy the components from us, it will make us very happy.

 

[Hi-Q]

Yeah, that doesn't really solve my problem.
Recommended footprints i do have (from manufacturer, JEDEC etc).
I also can make my own ones. The question is: How far can I shrink the pads but nevertheless get an acceptable soldering result?
Just to give some info ahead: Convection oven, air atmosphere, SnAg3Cu0.5

Regards,
Hi-Q

 

[stenzer]

Hi,

the used EDA program might also be of interest. E.g. for EAGLE there is a dedicated library available with smaller footprints for R, L and C. I think it is called “rlc-small“ or something like that. For a vapour phase oven based soldering I always achieved the better results with the smaller footprints, as there is less solderpaste applied and the components do not end as a tombstone (only soldered at one side and stick out from the board). The solder paste was applied with a stencil.

BR

 

[Carry for cents bazar]

No one can tell you for all components. You have to test. We have the standard pads, and we just use them. KiCad offers components with smaller and larger pads sometimes. Snapeda also.

 

[ZASto]

The footprints can be found at:
snapeda.com

You can always create the footprints by yourself. Google footprint SSOP exact dimensions or measure it with a ruler.

If you buy the components from us, it will make us very happy.

IMHO bolded seems inappropriate to the forum.
If you would like to advertise your company, do it some other way (usually you have to pay for AD )

 

[Carry for cents bazar]

Why? T here is no link and the forum rules are followed. On top of that I carry the responsibility for what I say. If you have any problem, you can always ask me. Also the paid advertisement is in motion, but it does not means that I can't test the fields and see from where to get customers first. Given the 1 person that viewed our site and bought nothing, its not looking good.

 

[BradtheRad]

SnapEDA website clarifies because it adds the word 'free':

Download free symbols, footprints, & 3D models for millions of electronic components

Since it doesn't ask for money to access that particular area it's in our readers' interest to allow mention of the website.

Edaboard sets aside the Business-Promotions-Advertising section for free posting of ads, allowing one ad per business per month.

 

[FvM]

I feel that the answers are not referring to the rather specific original question. It's asking if the manufacturer and IPC suggested SMT footprints can be reduced in size.

I'd give a rather general answer. You should not go below smallest IPC dimensions which are well substantiated. E.g. in case of rectangular chip resistors and capacitors, there should be a small positive "toe" distance. It allows the component to align during reflow.

On the other hand, you can use arbitrary footprint dimensions and are able to get working PCA in most cases. Production yield and reliablility - depends.

 

[cyberrat]

Have a look at the pcblibraries viewer, I think they still do a free viewer - it will give you the IPC7351 footprint sizes.
I think your looking for the "least" sizes.

 

[Hi-Q]

For a vapour phase oven based soldering I always achieved the better results with the smaller footprints, as there is less solderpaste applied and the components do not end as a tombstone

Thanks for mentioning that. It's interesting that smaller footprints can actually lead to better results in certan circumstances.

Have a look at the pcblibraries viewer, I think they still do a free viewer - it will give you the IPC7351 footprint sizes.
I think your looking for the "least" sizes.

Great advice. They actually have the Pro version free for some time. Don't know if I am really using Pro features, but I can play around with the recommended density settings and that's doing it for me.
I wonder if the heel always being zero for a 0805 resistor is correct, though.

I had also looked for thermal vias in pads underneath IC packages like DFN packages or SOP-like packages with exposed die pad and I found some publications where they tested various geometries and stuff like the thermal vias being tented or plugged or just plain open through hole vias. They checked for solder voids etc. and I thought that maybe there were also some publications about the results of experiments soldering chips with different pad geometries.
Like how many 0402 resistors can be put on a 12.7x12.7mm substrate

So if someone would know of something like that and could point me there, this would be a nice cherry on the martini.

Thanks again for your help

 

[FvM]

I wonder if the heel always being zero for a 0805 resistor is correct, though.

Correct according to IPC.