Electronics > PCB/EDA/CAD

Improvements in PCB top overlay (the white ink)

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VK3DRB:
Many times I have seen PCB's where the top layer white ink overlay has been crap. Like with writing software, consistency, clarity, ease of use and effective communications to the next poor bunny is almost everything. It is worth the extra effort to make PCB artwork look like it was done with pride. Here are some suggestions that might help others - you can agree or disagree. I would be interested to know of any other good practices others have used for top overlay.

(1) Pin 1 markers. Don't use circles on footprints at pin 1 markers. They look like fly vomit or soldered vias to those of us with challenged eyesight. Moreover, sometimes they are ambiguous between components for example when in a neighbourhood of SOT23s close together. A small slightly isosceles triangle as a pin 1 marker on a footprint stands out very clearly, even if it is tiny. It is unambiguous. No-one makes triangular vias and flies don't vomit up triangles.

(2) Wherever possible, place your component designators so the bottom of the letters are facing the component. If this cannot be done as in the case of a number of resistors "in parallel" next to each other, place the designator with the first character (eg: the R in R123) closest to its respective resistor. This tends to reduce ambiguity and confusion. Reading designators upside down is a mild inconvenience compared to guessing which SOT23 is Q12. Keep the designators, as far as practicable to the same font size, and of course, type.

(3) Make the character line thickness to 1/5 of the character height on non-TrueType fonts. This seems to yield the clearest characters for the average PCB. For example, a 1.5mm high character can have a 0.3mm line thickness.

(4) Keep designators at a consistent distance, as far as practicable, from component bodies. Spend some time aligning designators for equal spacing and offsets from the component bodies, so it looks really neat and professional. Neatly aligned designators impresses chicks.

(5) Back annotate so that the PCB designators are all relatively near each other in a logical pattern physically. Some people think this is bad practice, but there is nothing more frustrating when for example you cannot find R23, but can find R21, R22 and R24 amongst a sea of components. If this sounds trivial, just ask any debug technician how much time is saved when he can actually find components quickly and easily on a PCB.

(6) Use consistency in labelling. Make it look professional. Use smart abbreviations as required. Use underscores to join nearby words if it removes ambiguity. For example: "PWN IN PWR OUT" is much better written as "PWR_IN PWR_OUT". Labels for users to read may be larger than the component designators so they stand out.

(7) Mark the PCB next to connectors screw terminals with what the terminal function is. For example: "+5V  0V  -12V", and under it "POWER IN".

(8 ) When making footprints, make the outline of the component to avoid ambiguity and or mistakes when the part is inserted.

(9) Be aware of the PCB's manufacturer's capabilities. A quality manufacturer can print small fonts with clarity, whereas some cheapo manufacturer might just blur the characters. With good manufacturers, you may be OK using a serif font rather than a san-serif font.

(10) Use correct spelling. I have seen "RECIEVER" printed on a board (and in source code). If someone laying out a PCB cannot spell "RECEIVER", they should not have graduated from junior high school. There is no excuse for bad spelling. If you make typos like I do, have someone review your work.

(11) Have a library of marks and logos, such as RoHS and company logos etc as graphical components. Don't manually add them each time you do a board. It is a time saver.

(12) I could be wrong here, but use "REV 1" rather than "VER 1" Revision implies a sequence of modifications to the same product. Where version implies multiple versions exist at the same time.  I use "REV 1".

(13) Place as much instructions as practical and useful to the user on the board. Motherboard manufacturers are really good at this. Avoid having users read the manual for connections, which might be out of step with the PCB revision.

cheers,
Dave

hagster:
Good tips. Especially because inevitably you will end up building and fault finding your own circuits. On the other hand it's more fun to try and and obfuscate the PCB in devious ways. Here's some of my ideas.

1) always add an assortment of unpopulated components and connectors.

2) use case sensitive componant labels. R04, r04 and R4 can all be used on the same circuit.

3) if not critical to the circuit use the ground plane as a signal trace. And put a nice test point for someone to try and earth their scope to.

4) hide all vias under large components.

5) randomly make some switches pull up and others pull down.

6) use your own method of covertly marking diode polarity. Perhaps you could offset its label one way or the other or bring out obe track at 45deg.

I think the real trick is to do all this in a way that's easy for you to understand, but very tricky for anyone who doesn't know the secrets.

VK3DRB:

--- Quote from: hagster on December 23, 2013, 02:36:50 pm ---Good tips.
I think the real trick is to do all this in a way that's easy for you to understand, but very tricky for anyone who doesn't know the secrets.

--- End quote ---

I had a Russian colleague back in 2002 who deliberately wrote some of of his C++ code in Russian. He rarely commented his code and when he did, it was in Russian. After being allowed to do this for 2 years, he demanded the company pay him $180K per annum or else they would risk him leaving. :box:

Like with software, PCB reviews are mandatory in a professional environment, and bad practices would be weeded out before they become disasters. And like with software, any organisation should have software coding standards as well as PCB schematic and layout standards. :-+

Our PCB Design Standards is a 70 page document. It is clear, to the point and easy to read. One of the first things a new engineer gets to read when he joins the company is to read the C Coding Standards and PCB Design Standards.  :=\ The standards do not allow a free-for-all, but also do not impede intelligent creativity. Therefore the words shall, should, and may are used.    :clap:

marshallh:
I like your idea about triangular pin 1 marker, will start using it

nitro2k01:

--- Quote from: VK3DRB on December 23, 2013, 01:11:52 pm ---(1) Pin 1 markers. Don't use circles on footprints at pin 1 markers. They look like fly vomit or soldered vias to those of us with challenged eyesight. Moreover, sometimes they are ambiguous between components for example when in a neighbourhood of SOT23s close together. A small slightly isosceles triangle as a pin 1 marker on a footprint stands out very clearly, even if it is tiny. It is unambiguous. No-one makes triangular vias and flies don't vomit up triangles.
--- End quote ---
While I think this is a generally good idea, I'm not sure I agree With the ambiguity with a via. A filled via is bulgy and shiny, which means that you should be able to distinguish it by looking at it from different angles.

I've actually used this method sometimes, and speaking of round vias and potentially devious tricks, there's something I could do in a tight spot on the PCB I'm currently designing. I could make a pin 1 indicator in copper, over a via.

--- Quote from: VK3DRB on December 23, 2013, 01:11:52 pm ---(10) Use correct spelling. I have seen "RECIEVER" printed on a board (and in source code). If someone laying out a PCB cannot spell "RECEIVER", they should not have graduated from junior high school. There is no excuse for bad spelling. If you make typos like I do, have someone review your work.
--- End quote ---
I think this sometimes happens because the work has been outsourced to people whose native tongue isn't English. To be fair, English is not exactly consistent about these things; both ei and ie are used. Yes, ei is always used after c, but that requires the person to be familiar enough with the language to recognize this pattern.


--- Quote from: VK3DRB on December 23, 2013, 01:11:52 pm ---(12) I could be wrong here, but use "REV 1" rather than "VER 1" Revision implies a sequence of modifications to the same product. Where version implies multiple versions exist at the same time.  I use "REV 1".
--- End quote ---
To me, revision implies that something has been looked over from the original version, hence the re. So, the original version is not a revision, and the second version is "rev 1". What to use, imo, depends on the product line-up and target audience. If the products differ in market segmentation, I would prefer something like model A/B. (See: Dingleberry Pi.) If there are versions that are consecutive in time, but continue to exist side by side for some time, I would prefer version, and maybe even with a minor version number instead of a revision number. (So, version 1.2 or so.)

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