Dismiss
Is the New Reddit not your thing? No worries, time travel back to Old Reddit.
r/ECE
Find a community, post, or user
LO G IN
SIG N U P
r/ECE Posts
Posted by u/dvdlesher 4 years ago 2
COMMUNITY DETAILS
I got this PCB footprint intersection and another problem in Altium, help?
r/ECE
This is my first time designing something completely on my own (well, almost, there's my supervisor as well; I've asked him, but he is not very familiar with Altium, but he is familiar with EAGLE instead), so please bear with me if what I'm asking might be dumb. Quick summary of what I'm achieving: my project is about making portable accelerometer, powered by small sized solar panel (2cm x 2cm).
45.5k
114
Subscribers
Online
A subreddit for discussion of all things electrical and computer engineering. SUBSCRIBE
I have 2 problems with my PCB design, as shown in this image here 1. All the footprint seem to be intersecting with each other (Here's the zoomed-in version of U1 in the image.) 2. There is this big red unknown plane that I did not see in in my university course before, since the PCB files were half pre-made before, so I couldn't know what setting did they put beforehand. Could this be caused by "Power plane" setting in PCB Board Wizard?
CREATE POST
ADVERTISEMENT
The U1 footprint is given to me from the manufacturer page, although they did not mention about the PCB minimum clearance size of the wire in the data sheet. (datasheet: http://www.ti.com/lit/ds/symlink/bq25504.pdf) It seems that the 10 mil clearance is too much for this footprint, should I just decrease the size of the clearance? Also, one more thing, if I view the same footprint in the library, then there is no error at all with the footprint, as shown here, how come? Pardon for this barrage of questions and long text post, but I'm kinda stuck right now. EDIT: Thanks people, now I think I know what I need to do, but there are several more question that I need to clear up (still not answered yet): 3. Since the big red rectangle is just a room, what does the power plane setting actually do then? The way I made my power and ground plane in my previous uni subject was to use polygon plane (I'm not sure if this is the standard way to do it) 4. I noticed that in the U1's library footprint, there is this thin pink line which I can't click at all, so I assume that is not a track, and it's on Mechanical 13 layer. How do I make such line in Altium? Also, is that line actually important and necessary, or is that just for indication purpose? 19 Comments SORT BY
ADVERTISEMENT
100% Upvoted
Share
BEST
Sphere87 2 points · 4 years ago · edited 4 years ago
The red plane is a room. It is used in multisheet/multichannel designs where for example the components of each sheet is put in a room. This should ease laying out the PCB although I have never really been convinced about that. It certainly does not have any advantages if you only have one room. You can hide the room by going to the layer stack (LS button left from all the layer tabs) and then go to 'Altium Standard 2D', then Show/Hide tab and set Rooms to Hidden. If you keep the room it is advisable to lock its position because otherwise all the components might shift too if you move the room accidentally. The room does not have any other effect on your PCB, it's not copper or anything else. Just some helping tool for the designer to group components. When you create a new PCB design file there will be some default design rules set up. Apparently your design is violating some of these rules right now. It is up to you to decide whether the rules should be more loose or not. You will need to check with your PCB manufacturer for his capabilities. You base your design rules on that. You can change the design rules by going to design -> rules Share
About Careers Press
Advertise Blog Help
Content Policy | Privacy Policy User Agreement | Mod Policy © 2018 Reddit, Inc. All rights reserved
Save
BrokenByReddit 2 points · 4 years ago
This should ease laying out the PCB although I have never really been convinced about that. In my years of using Altium I finally used the rooms once for a multi-channel design. It makes duplicating a channel layout as easy as a couple clicks. I don't know if that's the best way, but it worked well. Share
Save
dvdlesher
1 point · 4 years ago
Multisheet is not the same as "more than 1 signal layer" is it? Anyway, fair enough, but it seems that the room size is larger than my board, I guess this is supposed to be the case? Also, based on what you said, I suppose deleting this big red rectangle should be fine, right? I think I'll try and keep it, but if it becomes too annoying, I'll delete it. Also, on the note of for the clearance, do they normally provide the minimum track clearance in the component's data sheet, or is there something like a universal "default" value for it? Thanks for the answer! Share
Save BAC K T O T O P
Sphere87 1 point · 4 years ago
The minimum track clearance (usually) depends on your PCB manufacturer, not the component manufacturer. If the track clearance is too small the manufacturer may not be able to fabricate your PCB. However for some chips the manufacturer might recommend clearance between some signals (e.g. high speed signals) to keep signal integrity (the exception to the usually). With multisheet I refer to designs where you use multiple schematic sheets tied together using a top-level design, Has nothing to do with the PCB itself. It should be fine to delete the room and the room-related design rules if that is not done automatically. Share
Save
dvdlesher
1 point · 4 years ago
Do you reckon a bluetooth transceiver chip is considered as high speed component? That's probably my main, important chip on my board at this point and is probably high speed. And if they would have their own clearance requirement, do you reckon that will be mentioned in their datasheet? Share
Save
BrokenByReddit 2 points · 4 years ago
Just delete the room, you don't need it. It seems that the 10 mil clearance is too much for this footprint, should I just decrease the size of the clearance? Yes. 10mil clearance is just a default and is too big for small SMT parts. Your design rules should match the capabilities of the PCB fabricator you plan to use. If they don't you run the risk of designing an impossible (or very expensive) PCB. Also, one more thing, if I view the same footprint in the library, then there is no error at all with the footprint, as shown here, how come? The footprint editor doesn't have design rules. Those are PCB-specific. Share
Save
thephoton 2 points · 4 years ago
If they don't you run the risk of designing an impossible (or very expensive) PCB. Just FYI for OP, with current technology you can reduce the minimum copper width and minimum spacing to 4 mil (0.004 inch) and still find many choices of places to fab the board. If you increase this to 6 or 8 mil, you will be able to reduce the cost if you shop around. Share
Save
dvdlesher
1 point · 4 years ago
Gotcha, basically bigger clearance is easier to make, therefore cheaper. Share
Save
thephoton 2 points · 4 years ago
Exactly. But above some point, the cost advantage is negligible. With current technology, that point is roughly between 4 and 6 mils. Share dvdlesher
Save 1 point · 4 years ago
To be fair, this component is pretty small already, I think it's about 3mm x 3mm, so I'm unsure about the track clearance, but I'll definitely ask the manufacturer. I've already asked this to different person, but do they (the manufacturer) normally provide the minimum track clearance in the component's datasheet? The footprint editor doesn't have design rules. Those are PCB-specific. Gotcha, thanks. Although I do find it strange that I need that same track clearance between Top/Bottom layer and Top/Bottom Overlay layer. I thought they shouldn't matter since the Top Layer is ultimately the one printed with copper, whereas the other one is not? Share
Save
BrokenByReddit 2 points · 4 years ago
do they (the manufacturer) normally provide the minimum track clearance in the component's datasheet? No. The datasheet just tells you the dimensions of the part, and sometimes the recommended footprint. You get the minimum clearance from the place that makes your PCBs. They should have all that info on their website (minimum trace width and minimum clearance usually being the most important ones). I thought they shouldn't matter since the Top Layer is ultimately the one printed with copper, whereas the other one is not? Not sure what you mean by this. There's a rule for copper to overlay/silkscreen clearance so you don't put your silkscreen text over pads, making it illegible on the finished board. Share
Save
dvdlesher
1 point · 4 years ago
No. The datasheet just tells you the dimensions of the part, and sometimes the recommended footprint. You get the minimum clearance from the place that makes your PCBs. They should have all that info on their website (minimum trace width and minimum clearance usually being the most important ones). Their website have that information instead? Well that explains why I'm having trouble finding that information Not sure what you mean by this. There's a rule for copper to overlay/silkscreen clearance so you don't put your silkscreen text over pads, making it illegible on the finished board. Ah, that's exactly what I mean. Thanks man, I wasn't aware that there is a clearance specifically for silkscreen as well. Share
Save
BrokenByReddit 3 points · 4 years ago
Their website have that information instead? Well that explains why I'm having trouble finding that information Please forgive me if I'm being patronizing but it sounds a bit like you're missing the point here, but maybe I'm misunderstanding you. TI makes your chip. Everything you need to know about the chip itself is in the datasheet. TI doesn't know anything about what kind of PCB you're putting it on. Someone else makes your PCB. You get the clearance info from the place that makes the PCB, because that varies from one PCB fabricator to another. It's their manufacturing capabilities and tolerances. Share
Save
dvdlesher
2 points · 4 years ago
Wait a minute, I think you might be right about me misunderstanding you. So the company I should be contacting about the track clearance is the the one the makes the PCB board, not TI itself (in this case)? If that was the case, then let's assume for example a company named X told me that I can set the clearance to 5 mil, does that mean there is no restriction at all from TI side? Share
Save
BrokenByReddit 3 points · 4 years ago
So the company I should be contacting about the track clearance is the the one the makes the PCB board, not TI itself (in this case)? Yes. Here's an example from OSHPark. Under "Design rules:" 6 mil minimum spacing at least 15 mil clearances from traces to the edge of the board 13 mil minimum drill size 7 mil minimum annular ring All of these should obvious except for the last one. This image pretty simply shows what the annular ring is. Lots of other good stuff on the source page too. If that was the case, then let's assume for example a company named X told me that I can set the clearance to 5 mil, does that mean there is no restriction at all from TI side? Correct. TI already sold you a chip, they don't care what you do with it. Share
Save
dvdlesher
2 points · 4 years ago
Thank you very much, that was very helpful. And no, you didn't sound patronizing at all. In fact, I am very thankful that you corrected me. Share
Save
BrokenByReddit 1 point · 4 years ago · edited 4 years ago
3. Since the big red rectangle is just a room, what does the power plane setting actually do then? The way I made my power and ground plane in my previous uni subject was to use polygon plane (I'm not sure if this is the standard way to do it) Power planes are for when you have a 4+ layer board. Then you can dedicate one layer to VCC (or multiple power supplies) and one layer to GND, and just drop a via wherever you need a connection. Altium understands this so when you have a plane layer, it knows that you want copper everywhere on that layer except for where it has to be taken out to avoid shorts. Basically it will draw it in reverse of a normal layer. 4. I noticed that in the U1's library footprint, there is this thin pink line which I can't click at all, so I assume that is not a track, and it's on Mechanical 13 layer. How do I make such line in Altium? Also, is that line actually important and necessary, or is that just for indication purpose? If you used a wizard to generate this footprint, it's probably a component body. If I remember correctly, the wizards put 3D bodies on Mechanical 13 by default. If you go into 3D mode (hit the "3" key, then 2 to go back to 2D) does it show you a grey block where the pink outline is? BTW, you can't make zero-width lines in Altium. You can make very thin lines that will be super hard to click... but you shouldn't! Share
Save
dvdlesher
1 point · 4 years ago
If you go into 3D mode (hit the "3" key, then 2 to go back to 2D) does it show you a grey block where the pink outline is? Not really, it only shows the pads and that's it. But anything on Mechanical layers will be ultimately ignored in manufaturing process, right? I assume they are there only for indication/simulation purpose and that's it. Share
Save
BrokenByReddit 1 point · 4 years ago
You can use the "PCB List" and sort by layer to see what they are. But anything on Mechanical layers will be ultimately ignored in manufaturing[sic] process, right? You can choose not to generate Gerber (manufacturing) data for those layers, yes. Share
Save
The Reddit App Reddit Gold Reddit Gifts
