Eagle footprint

[Wilksey]

Hi John,

Looks pretty good from here!

Do you have any tips for drawing the footprints? I would quite like to have a go myself, for instance I couldn't really see what size the pads are supposed to be, and how you work out the distance and offset between the horizontal and vertical and centre pads, and had you not have mentioned it I wouldn't have noticed the RF pad a different spacing to the others!

Many thanks again for all of your help! Really is appreciated.

Wilksey

 

[jpanhalt]

Most of the time, I find a package for a different device, copy it and make whatever edits are needed. In this case, that was not possible. Drawing to exact dimensions in Eagle is cumbersome, but not that hard. It is nowhere near as easy as a CAD program that lets you use referencing.

In this case, I set up two grids as the pads were on different centers. Be sure the grids are consistent (i.e., 0.05 is a common divisor of 1.0 and 1.2). Some people like a very fine grid for the alternate. I do not. My skill with an optical mouse just doesn't allow it, so having the advantage of parts and lines snapping to 0.05 grid rather than something like 0.0001 was a help. Eagle automatically centers the pads. I then set up some drafting lines in "document". That helped align everything. Finally, you have the measure function. I zoom in on the part quite close, set the reference, and then can get quite accurate. If all else fails, you can change the coordinates in the Information dialog. It is also good to watch those coordinates to tell a small difference, such as 0.88 vs. 0.89 mm in a location or length. I think a lot of things can be done in the command line. I am not very good at that, but Boncuk (a member here) is.

Finally, for making the t-Doc slots (stencil), I made a pad of the right dimensions. Set the alternate scale to what would be needed (i.e., 0.89 mm needs 0.005 mm for the alternate so it can be centered on a grid line). Then trace the pad with the rectangle tool and the correct layer. You then have a perfectly centered stencil that you can put on each pad as needed.

What took the most time after getting the dimensions right (I hope ) was the crazy numbering scheme and the absence in the datasheet of a top down view with the pins numbered.

John

 

[Wilksey]

Hi John,

I shall probably have a go at making the footprint myself, at least I have a correct one to reference against, I guess it is just a long hard study of the datasheet and it's dimensions! And of course the grids etc.

I have never had to use the stencil stuff before, nor had to set up anything for a solder mask, what layer is the solder mask on? I take it the stencil is the area that the solder paste will be applied to?

Thanks,
Wilksey

 

[jpanhalt]

To be honest, I am not absolutely sure what layer is the solder mask. I have never used a commercial house to make my boards. I believe the solder mask may be "t-stop" and "b-stop."

Yes, the stencil is for the solder paste.

Maybe Hans (Boncuk) will chime in. I think it is great you want to learn to do it yourself. Let us know if you get stuck on anything. If you do it often, the command line is a great resource. I used it to set up a template for my special function keys (F keys). That really helps especially in doing boards. I rarely use the auto-router.

John

 

[Wilksey]

Ah yes, top and bottom stop layers, sounds like it could be it, do you know what the "cream" layers are used for?

Well, although I appreciate what you have done for me I would have much preferred to do it myself, but I just don't have the confidence in reading the data sheets and drawing the part, any help will of course be greatly received, I prefer the command line over the GUI buttons when drawing anyway so I will almost certainly stick with that.

Would you mind sharing how you learnt to do it? Because you really did knock that part up in no time at all really!!

Thanks

Wilksey

 

[jpanhalt]

I started with Eagle 3.xx and my first purchased program was 4.1. That came with a nice booklet that I still have. This link may be the same thing:

**broken link removed**

There are now more popular tutorials. The ones on Sparkfun are often recommended:

https://www.sparkfun.com/tutorials/110

Most people moving to Eagle comment about the learning curve. For example, versions before 6.0 used cut (scissor icon)/paste. The copy utility was just for components. The cut action actually is copy without deletion. It does not act at all like "control X" in a word processor. Version 6.0 changed that to be more consistent with usage in Windows and other programs. However, 6.0 does allow one to revert back to the previous dialog. I tried the new copy routine and immediately went back to the older version. In other words, you may find some of the Eagle controls a little different, but once you get used to them, you can do almost anything. And as mentioned above, if you are doing Eagle frequently, learn to use the command line. I tend to get immersed in a project and then do nothing for 6 months or more. While I am involved actively, I usually relearn some of the commands. They really extend the utility of the program.

As for learning to make parts, just try it. Once you get one done, it will seem simple. Nevertheless, drawing complex designs, particularly with irregular pin spacing, is more challenging.

As for the t/b-cream layers, they are mapped to Gerber layers 31/32, but I could not find a simple chart relating the names to the function in Gerber. One source said cream was the plated area on pads. Another said it was for the solder paste stencil. In the device we just finished, you can see they are similar.

I suspect cream is the plated area of the pad. The solder paste mask may be identical, but it may also be different for smaller or more cramped packages. Try this in Eagle. From the control panel, open library > microchip.lbr > package > TQFP100 (a device similar to yours). Note that t-cream (31) covers almost the whole pad, but t-Docu (51) only covers the inner portion of the pad. I suspect from that example that layer 51 is for the solder paste and layer 31 is for plating.

John

Edit: Here's another link. It implies that cream was for solder paste, but in more crowded devices, like QFN, one needs to use a smaller pattern.

https://blog.screamingcircuits.com/2011/11/qfn-custom-stencil-layer-in-eagle.html

For your device, you may want to use a smaller cutout in the stencil for paste as specified in the datasheet for thick stencils. If you need to change it and want to give it a go yourself, I can help you over any rough spots.

 

[Wilksey]

Hi John,

Many thanks for all of the links and advice, time is not on my side at the moment but I hope that in the next few weeks I can get some time to start my new project.

I shall have a go at creating the footprints and I shall read and re-read all of the tutorials, may take a month or so to get to the stage where I am comfortable designing the footprints etc, but I am also finding it difficult interpreting the drawings for complex footprints, do you have any tutorials on how to go from drawing to footprint (doesn't have to be Eagle, the concept will be the same).

Thanks

Wilksey

 

[jpanhalt]

Regarding dimensions, all I can say is that I am not very knowledgeable about them. I am neither an engineer nor a draftsman. I did have a drafting course in high school and have learned to use programs such as Graphite (Vellum) and SolidWorks.

When you talk about dimensions on parts, there are parts that are underdefined. That is, there is no way to calculate all of the dimensions from what is given. The stencil plan in your recent project is an example of an underdefined drawing, unless one includes the fact that it needs to fit over the pads. The pad drawing was fully defined. But even then, one must guess to which end of the pad, the stencil cutout should be.

Then there is the over-defined or over-constrained drawing. An example would be if you had three segments and showed the length of each segment and the total. If you do that, SolidWorks will give you a warning. Obviously, one dimension can be deleted, so it is "over-defined." But, as an amateur machinist, I think it is well defined. I always add in extra dimensions I might need while making something in the shop to avoid making calculations on the fly.

My conclusion about dimensions is that there are strict rules and then there are practical rules. You will usually see pad layouts tend to follow the strict rules of not being over-dimensioned. But, going from that to a practical layout is just a matter of adding and subtracting.

I have never seen a tutorial on how to calculate dimensions from a drawing, but then again, I have never looked for one.

John

 

[radhikapatil]

[MODNOTE]Deleted Off Topic[/MODNOTE]

 

[Tru]

What the hell, I registered to download this zip file (TempETO.zip) and all I get is a useless blank page with no content.
Trying to download the file using the link results in a generic html. from what I can see so far this site sucks.

 

[jpanhalt]

What the hell, I registered to download this zip file (TempETO.zip) and all I get is a useless blank page with no content.
Trying to download the file using the link results in a generic html. from what I can see so far this site sucks.

This explains it. No need to throw a tantrum.

https://www.electro-tech-online.com/threads/server-down-hard-drive-failure.131876/#post1104452

John

 

[Ian Rogers]

Tru... What link did you follow?

 

[jpanhalt]

Tru... What link did you follow?

Which "you?"

The original link to the footprint I designed does not work, as the attachment for that post is apparently lost. In this case, I also didn't keep the design on my PC's as it was exceedingly unlikely I would ever use that device.

John

 

[Wilksey]

Original file

Hi,

I really don't think that being rude is the way to go about things!

John was exceptionally kind in creating this component for me in the first place and I was in two minds about uploading the file because of your attitude, but I thought there may actually be someone else who appreciates his work as much as I do and want to download it.

Please don't be disrespectful to the people on this site, they are a great bunch of people and this site really is a gold mine if you took the time to use it properly! Also I might remind you that people use their own time to help others out here, and they could quite easily charge for what they provide for free!

So please show some respect!

Thank you.

 

[Ian Rogers]

Which "you?"

The original link to the footprint I designed does not work, as the attachment for that post is apparently lost. In this case, I also didn't keep the design on my PC's as it was exceedingly unlikely I would ever use that device.

John

Sorry John I was directing it at Tru... I was going to look for the info... But Wilksey to the rescue...

 

[jpanhalt]

@Wiksey
Thanks for re-posting the design. There was no trace of it on the PC I used, because of the way I keep and delete test files.

John

 

[Wilksey]

Absolutely not a problem, glad to be able to give something back!

Wilksey

 

[Tru]

The original TempETO.zip link.

I was interested because soon I will have to lay out a footprint for a 144 pin LGA device from Telit.