QFN-20 ? Need help for component


#1

Can someone help me ? I need a component with QFN-20 so that I can create my board. Many thanks in advance Greetings Marc

Kann mir jemand helfen ? Ich brauche ein Bauteil mit QFN-20 damit ich meine Platine erstellen kann. Vielen Dank im vorraus
Gruß Marc


#2

You need more than just the footprint usually. What part are you trying to use in QFN-20? That said there is a QFN-20-0.4MM_pcb.svg footprint in core parts (your_fritzing_directory/fritzing-parts/svg/core/pcb/QFN-20-0.4MM_pcb.svg) if that does what you need.

Edit:

As well typing qfn20 in to the parts search bar comes up with 3 or 4 parts that use a qfn20 footprint.

Peter


#3

Thank you for the fast answer! I need it for this ic:
https://www.mouser.de/ProductDetail/Silicon-Laboratories/SI4713-B30-GM/?qs=p9T7GgSe1IGVk099WRQKaw%3D%3D&gclid=EAIaIQobChMIrfPj2_-y4AIVkOd3Ch0G7wX9EAAYASAAEgLZnfD_BwE

Regrads from germany


#4

It doesn’t look like the stock footprint will do it. It lacks the ground pad and the recommended footprint is quite different. I can make you a part but it will probably be tomorrow as it is late here already. I’m going from the footprint in the data sheet here:

https://www.silabs.com/documents/public/data-sheets/Si4712-13-B30.pdf

and the stock footprint looks like this:

Untitled%20Sketch_pcb

which is fairly different (and at rf probably matters).

Peter


#5

That would be great ! No problem i can wait a few days
Thank you very much :slight_smile:

Regards


#6

Almost there, unfortunately almost only counts in horseshoes. There are a couple of problems: the small pads seem to be too small for Fritzing, the trace doesn’t connect: (for a miracle the forum actually liked this svg from gerbv, right click on the image and save image as will get you a copy to bring up in an svg editor so you can see it.

gerbv_output

this is a png from fritzing which shows the other problem: the pads which look fine in Inkscape are all piled together in Fritzing the one on the left is your part, the one on the right is an earlier small qfn I made for someone else (who actually managed to hand solder the chip on to there, there are pictures in the forum post!). I suspect this is because I used a path for the pads on your part (which i haven’t done before) and there may be something wrong there. I can fix the non connection by making the square pads in to a rectangle like their neighbor, but it won’t match their recommended footprint. In any case I’ll keep poking (and maybe someone better at boards that I will have some suggestions).

test%20Sketch_pcb

Here is the sketch with the two parts (they will be in the temp parts bin) as well
the Si4712/13-B30 part is complete other than the non functional pcb.

edit:

It would be useful to upload the sketch before posting …

test Sketch.fzz (23.6 KB)

Peter


#7

Those corner pads aren’t very nice.

If he is soldering them at home they will have to be extended, like the others, so you can wick solder to them.

The FZ looks touching, but the gerbers show separation.


#8

Fixed my problems. There was a stroke length on the paths which is what was bothering pcb view, it looks like too small pads aren’t supported in Fritzing so I extended the four small pads to be the same length as the paths and now it works.

good%20Sketch_pcb

The ground pad is connected by a via and a trace on the bottom layer. The gerbv image is a bit ratty even with rendering high:

good_gerbv

again an svg image, right click and save as to get a copy. Finally the finished part and its test sketch. Note as always you need to print out the footprint and verify it against a real part before ordering boards (may be difficult in this case though). The default DRC rules have a fit with this part, I expect you will either need to be careful or figure out how to loosen the DRC rules.

FM_Radio_transmiiter.fzpz (10.2 KB)

good Sketch.fzz (27.5 KB)

Good luck (soldering this will be fun :slight_smile: ! )

Peter


#9

Thank you very much i will test it the next two days and let you know :blush: very much thanks for the big help

Regards from germany


#10

Hey Peter, i have now test it.

the fzpz looks perfect but it´s mirrored because when i set “top view” and i look in the data sheet then it´s wrong. Can you check this and let me know ?

regards from germany

Marc :wink:


#11

To make sure I have this straight: in pcb set to view from top and in Inspector pcb layer is set to top (both of these are important, because if the pcb layer is set to bottom for bottom of the board the part will be mirrored) the chip pins are mirrored. It is possible I’m wrong because the data sheet has one drawing top down and the one beside it bottom up and I may have reversed them. It is also a little unclear on which one is pin 1, I think it is the small pad.

Edit:

It appears correct to me as is. It appears to match figure 23 in the data sheet referenced above. Note figure 22 just above it which also has pin numbers is top view on the left and bottom view on the right. Although that isn’t stated, the pin numbers are mirrored between the two pictures which explains which is which.

Peter