EE’s Dilemma – Design Parts or Boards

Most engineers would rather design PCBs than libraries. But how can you trust a library with other contributors?

Whenever I talk to electronics designers about what they dislike the most when it comes to creating electronics the answer is almost always the same. Part creation. It doesn’t matter if I’m talking to an experienced designer who’s been doing it for years or to a beginner whose been at it for 3 months, people don’t like “wasting” their time creating their components. Why is that?

There seems to be three basic reasons as to why people don’t like create their own components:

  1. Footprint, Symbol, 3D model Styles
  2. Trust
  3. Time

What if there was a way to solve all these issues and create a centralized database that we can all trust, agree on styling, AND not spend time creating? It may sound like a dream but I don’t think so, I think this is something completely within our grasp. Come with me and I will take you to the promised land.

Footprint & Symbol Styles

The first thing we need to do is to figure out how to solve the problem of style. We all have our preferred way of doing things, a way we like to view our schematics and boards. I propose we do the same thing that schools and the military do, uniforms. We take away the personalization of part creation and create a standard.

Now this isn’t a new radical idea, in fact its an old stale one but somehow it seems to be forgotten.  Way back in 1975 IEEE created the standard IEEE 315. This standard was made to fix this exact issue of how schematic symbols should look. I’m not sure exactly what happened but somewhere along the way people went their separate ways. It could be a new generation of designers or maybe people just didn’t want to change, either way that’s not the point. This standard was made for a reason and it should be followed.

The IEEE 315 standard is extremely comprehensive, so much so it includes schematic symbol elements allowing you to symbolize parts that haven’t even been invented yet. Let me explain. IEEE 315 gives a standard to construct any symbol, every line, dot, and feature has a meaning. With these tools available, one is able to construct any symbol for any possible component that does or does not exist.

IGBT Symbol Meaning

The next thing that we as designers need to come together on is the footprints / land patterns / decals for components. Just like with schematic symbols we don’t have a standard that we all are using despite there being a standard out there available to us. That standard is IPC-7351. IPC-7351 provides information on land pattern geometries used for the surface attachment of electronic components. This includes things like sizing and tolerance to insure there is sufficient area for all the appropriate solder fillets.

Caliper and CPU

So far we’ve taken a look schematic symbol and PCB footprint standards but there’s still one thing missing and that’s a standard for creating the 3D STEP model. And yes there is a standard for that as well, isn’t that great!? The standard for that is the JEDEC Publication No. 95. JEDEC 95 describes the dimensional and geometrical characteristics of “standard” component packages.

JEDEC_MO-012

Trust

Okay, so we’ve talked about how to standardize on schematic symbols, PCB footprints, and also 3D models. But what about the trust and time issue. We solve the trust issue by applying these standards. Once everyone or most people apply these standards to part creation as they should, we can all have a higher confidence that we’ve all done things correctly.

Of course nothing a person does is without error all the time. This is why we need an online database with everyone uploading their component models. And to be sure all components are up to standard we can crawl and verify each component as they’re uploaded. In addition to software verification, having users review and use components will give everyone a solid indication of which part is good and which is not.

Time

As you probably have guessed having this online database where users and professionals can upload their component symbols and models will save time, for everyone. It may surprise you but this isn’t a fantasy, well not completely. EE Concierge is a service that will create a complete component for you including schematic symbol, PCB footprint, and also a 3D model. The EE Concierge component making process follows the above industry standards so you know what you’re getting is correct and transferable to anyone. As for an online database filled with components, that’s where Octopart comes in. Octopart is a search engine for electronic components and industrial products. It includes things like a BOM scrubber, pricing and a bunch  more. It’s definitely worth checking out.

 

28 Basic PCB Design rules

28-pcb-design-rules

These 28 Basic PCB design guidelines set out best practice to reduce the cost of your boards and to minimize the risk of errors arising during manufacture.High power boards have different rules especially in terms of spacing, traces size and power isolation. Manufacturers have different requirements; make sure you read their own guidelines before sending your design. Naming and file formats also vary depending on the manufacturers.

PCB Layout

1. Create your board frame on a 0.05″ grid. Make the lower left corner start at 0,0.

2. Usually the board frame is rectangular. For specific reasons you could also do other types of shapes such as polygons.

3. Stick parts on a 0.05″ grid. You should not break this rule unless you have a very good reason.

4. Any LED should be labeled with its purpose (power, status, D4, Lock, etc).

5. Idem for connectors: e.g Vin, Port1, Batt, 5V, etc.

6. Idem for pins where applicable: e.g TX, Power, +, -, Charge, etc.

7. Idem for switches and switch states: eg. On, Off, USB etc.

8. When applicable, it is better to avoid having vias go through the silkscreen when adding labels.

9. Group components together. For example the resistors surrounding a transistor in your schematic will also be grouped together on the PCB.

10. Minimum drill size should be 15 mil.

11. Minimum annular ring size should be 7 mil.

12. 7 mil is the minimum size for traces. 8mil is acceptable. When possible try to keep the traces size to 10mil.

13. Use thicker traces for power lines. 12mil=100mA max, 16mil=500mA max etc.

14. 7mil between traces and space is reasonable.

15. Avoid 90 degree corners. Straight lines with 45 degree corners are preferable.

16. Where applicable use a ground pour on top/bottom layers.

17. To prevent pours from shorting to traces make sure you use a 10mil isolation setting on any of the ground pour.


Schematic Layout

18. Use a GND symbol for all the GND connections.

19. Use appropriate power symbols for All VCC, 5V, 3.3V etc.

20. Add color notes to separate a complex design into various smaller bits (for example,charge circuit, accelerometer, etc).


Footprints

21. All footprints need a reference designator {{refdes}}. If you come across a part on a board that doesn’t have this, you should change it and save the library. For parts requiring it a pin one marker should be defined.

22. All footprints need silkscreen indicators showing mechanical sizes, dimensions, or anything wired about the part.

23. To prevent it from flaking off easily silkscreen within a footprint or board should not go over pads or metal that will be exposed.

24. Top component layer should be marked by a red centre cross.

25. Package outline layers should outline the actual package size.

26. The Top Courtyard layer should include all of the pins.

27. When adding a footprint make sure you add a solder mask.

28. Every new footprint and part will have a human readable description.

 

Feature Announcement: Upverter Gets Your Circuits Laid!

Screen_shot_2012-11-02_at_3

AKA: Announcing Layout, Footprint Generation, And Gerber Exporting

It’s finally here! We have spent the better part of the last year building the worlds most sophisticated layout tool. And it does everything you’ve asked for and more! We started work on it back in November 2011, launched it into private testing about 6 months ago, and have already exported and manufactured hundreds of boards. And its finally rock solid, and ready for prime time.

Here are the improvements:

  • PCB Editing! Woot!
  • Support for infinitely many layers (some mfg limitations)
  • Support for infinitely large boards (some mfg limitations)
  • Full real-time design rule checking
  • Multi-editor collaboration just like our schematic tool
  • Same time schematic & PCB editing… for the first time ever… like in the world… first. time. ever…. this is a pretty big deal.
  • A system of automated footprint generators based on the IPC standards
  • A custom footprint editor for connectors and non-standard parts
  • RS274-x Gerber exporting (that actually works, and are manufacturable)