PDA

View Full Version : Looking for Recommended practices for schematic/PCB/BOM design



Timothy D. Swieter
07-11-2006, 01:17 AM
I am an engineer and like to design things to capture all the information in a logical sense. I have been doing industrial control system design and drawings for a while. On the assembly drawings (the drawing that shows how to mount components within an enclosure) there usually is the Bill of Materials. Then there is a schematic drawings that details the wiring of the cabinet.

Now I am getting more into schematic/circuit/PCB design at my work. I am glad that I have the electronics/robotics skills from my hobby, but lack someone to show me the way for doing things professionally (clean, neat, and in some recognizable fashion to the industry).

I am interested in learning more about recommended practices (or what others do) to document their design. Does a BOM get placed on the circuit schematic drawing? If not on the schematic, where then? Separate Excel sheet? In addition to the Gerber files is a drawing created for the board layout? I like to keep things simple and make sure all the information is documented and presented in a logical manner. At the moment I don't see how a circuit and PCB design is documented cleanly, how curren design has the information spread across too many files.

I thought I would ask the more experienced circuit/schematic/PCB designers on this forum. Thank for your thoughts.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Timothy D. Swieter
tdswieter.com (http://www.tdswieter.com/)
------------------------------------------------------------
One little spark is all it takes for an idea to explode

Kevin Wood
07-11-2006, 01:27 PM
I highly suggest that you implement some type of source control system. They're typically used for software development, but there's no reason that you can't use them with CAD, BOMs, etc. It makes tracking changes & revisions much easier. Also, put everything in the SCM system.

You could check out SubVersion for open-source, or Perforce for commercial. Also look at O'Reilly for books on source control.

Loopy Byteloose
07-11-2006, 08:46 PM
I used to build homes and worked in many construction contracting roles.
The usually proceedure is to annotate the plans.

Version numbers are quite important to immediately get people to comprehend where problems lie.

Since I use Eagle for schematics and PCBs, I merely add, in the schematic, a line of text that includes the date, the version # change, and the summary of change. I also provide a version # in my Title at the page top.

Then, I use the same text feature and provide the Version # as part of the actual copper on the circuit board.

Windows Office provides all the document management features that most would ever want. The main thing is to find a system that allows you to enjoy maintaining it. Otherwise, you give up when it begins to feel like a huge waste of energy and time. Feel free to only use 10% of a complex system and use it well.

Someone once told me, 'There is Need-to-know; Nice-to-know; and Garbage.' I have always appreciated that bit of wisdom.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"If you want more fiber, eat the package.ˇ Not enough?ˇ Eat the manual."ˇˇˇˇˇˇˇˇ


ˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇ Tropical regards,ˇˇˇˇˇ G. Herzog [ˇ黃鶴 ]ˇin Taiwan

Forrest
07-12-2006, 01:10 AM
A typical drawing package for an assembled PCB is:
1. Board Fabrication drawing (PDF)
2. Board Schematic (PDF)
3. Gerber files for all layers including circuit layers, solder mask, silk screen and solder paste (RS274X)
4. Drill file (1 for plated thru holes and 1 for non-plated thru holes) (Excellon)
5. Bill of Materials (text or Excel)
6. Board Assembly drawing (PDF)
7. Readme file that lists the file name and description for all the files and a contact name and phone number for questions (text)

Zip these files and send them to your board fabricator and/or assembler

John R.
07-12-2006, 01:50 AM
Forrest,

What does the designation (RS274X) stand for? I understand the contents your describing on line 3, just wanting to educate myself.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
John R.

8 + 8 = 10

Timothy D. Swieter
07-12-2006, 06:17 AM
Forrest - I understand most of the things you mentioned.ˇ What is the difference between the Board Fabrication Drawing and the Board Assembly Drawing?ˇ Why not include the BOM on one of these drawings?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Timothy D. Swieter
tdswieter.com (http://www.tdswieter.com/)
------------------------------------------------------------
One little spark is all it takes for an idea to explode

Forrest
07-12-2006, 07:28 AM
RS274X (also known as extended Gerber) is a way of describing pads, circuits, etc. Older CAD/CAM systems from 10-30 years ago used an older format called RS274D. RS274D requires a seperate aperature list and only supports raster fill patterns. RS274X contains the aperature list, supports raster and vector fill patterns and also supports custom aperatures. For more info see www.artwork.com/gerber/274x/rs274x.htm (http://www.artwork.com/gerber/274x/rs274x.htm)

A board Fabrication drawing is used to build the bare printed circuit board (no components) and includes this like a drill table listing codes and drill sizes, mechanical dimensions of the board, board thickness, laminate requirements, plating requirements and test requirements.

A board Assembly drawing shows the board outline and component references. locations and polarity and any special assembly notes. It's typically created by overlaying the board outline, soldermask and silk screen layers in your CAD program. Some examples of notes include maximum lead protrusion, LED heights, and heat sink/fan assembly.

The BOM is never included on the drawings for 2 good reasons. One - you can't place an online parts order using a drawing. Two - it's very common for a single board design to perform different functions if it's assembled with different components. For example - let's say you designed a Basic Stamp motor controller board that can be driven from a PC or daisy-chained from another Basic Stamp motor controller. In the first case the board would be fully populated with RS232 to TTL circuit including transistors, resistors and capacitors. In the second case, you could omit the RS232 to TTL circuitry.

Timothy D. Swieter
07-12-2006, 07:58 AM
Thanks for the response.

For your reasons why to not have the BOM in a drawing I can understand the first reason. The second reason I would create a tabulated table in the drawing. Of course having an Excel BOM and a drawing BOM creates more work to keep things updated.

For designs that we have done I guess we have never really done a board assembly or fabrication drawing. We drew the circuit/board in Electrnic Workbench and then sent off the Gerber files. My current project I think I need to document the design better than our past projects and will pursue doing an assembly and fabrication drawing. Do you have any examples that you wouldn't mind sending to me as reference?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Timothy D. Swieter
tdswieter.com (http://www.tdswieter.com/)
------------------------------------------------------------
One little spark is all it takes for an idea to explode

Forrest
07-12-2006, 11:07 AM
Here's a typical Board Fabrication Drawing www.datacircuits.com/docs/Fab%20Drawing%20Sample.pdf (http://www.datacircuits.com/docs/Fab%20Drawing%20Sample.pdf)
Note page 2 shows breakaway rails - typically added to support a board thru wave soldering thru hole components

Here's a link to a Freescale reference design that includes Board Fabrication and Assembly drawings
www.freescale.com/files/soft_dev_tools/hardware_tools/schematics/MC56F8367EVMBAG.zip (http://www.freescale.com/files/soft_dev_tools/hardware_tools/schematics/MC56F8367EVMBAG.zip)

Loopy Byteloose
07-18-2006, 12:43 AM
Forrest's list is quite good, but I wonder if a PDF format is truely needed. Can't you just do the same in MS Word and protect the file from changes?

While PDFs are neat and very professional, it is just one more overhead expense in getting started.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"If you want more fiber, eat the package.ˇ Not enough?ˇ Eat the manual."ˇˇˇˇˇˇˇˇ


ˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇ Tropical regards,ˇˇˇˇˇ G. Herzog [ˇ黃鶴 ]ˇin Taiwan

SteveW
07-18-2006, 01:21 AM
Hold on a minute - you _paid_ for Word, yet worry about the (zero) cost of generating PDFs?
I am never happy to receive word documents from customers, since there are likely version problems if they're using the latest version, or virus / macro issues. Just use OpenOffice and export PDF directly - no pain, no worries.
The last version of Word (or office, of any sort) I bought was 95, and I don't miss it at all. PDF is definitely my favoured formatfor handing documents like this around, if it doesn't have to be imported into a CAD package.

(Also, for what it's worth, if I'm using an assembly shop, I like to send either a sample, or a high res scan of an assembled prototype)


Steve

matthelm
07-18-2006, 01:25 AM
Kramer said...
Forrest's list is quite good, but I wonder if a PDF format is truely needed. Can't you just do the same in MS Word and protect the file from changes?

While PDFs are neat and very professional, it is just one more overhead expense in getting started.


Do what?ˇ PDF printing is free, where Word cost $$$!ˇ Plus anyone with an internet connection can read PDF (on almost any platform) while Word has limited support.ˇ Plus Word captures graphics as bit maps, which really sucks when you want to zoom in to see every detail, or will be REALLY large, while PDFs are rendered as lines with thickness, and can be viewed at all scales and plotted at any size.

You did see that all those PDFs were "drawings" not documents!




Post Edited (matthelm) : 7/17/2006 5:29:07 PM GMT

StarMan
07-18-2006, 03:50 AM
One additional comment about pdf's.ˇ They areˇsnapshots of evolving documents.ˇ I use them as an archiving tool.ˇ By including the revision level in the name each time I save it, I have a complete revision history of a design.

Chris I.

Loopy Byteloose
07-18-2006, 10:48 PM
I will have to take another look, but I thought you had to get an Adobe licence for $$$ to create PDFs. Just the reading side is free.
Are you saying that everything is free?

Yes, I am a proud owner of Microsoft Office 2003 with all its baggage.

I live in Taiwan and there isn't but a few expats to discuss computers with. 99% of Taiwan had been operating on Windows95 without licence until WindowsXP managed to come bundled with all the hardware. Taiwanese use the Chinese version of window which have Chinese characters [16bit Unicode] in the DOS files.

When I buy a computer I get the WindowsXP Chinese version and it is really a pain to try to read all the configuration and support in a language that is relatively new to me [been studying for 12 years].

Forgive me, but I just needed something that was English, licensed, and supported overseas. It is buggy and I do have to run 3rd software to protect it and clean up its trash.

Does OpenOffice handle both Chinese and English in the same text?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"If you want more fiber, eat the package.ˇ Not enough?ˇ Eat the manual."ˇˇˇˇˇˇˇˇ


ˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇ Tropical regards,ˇˇˇˇˇ G. Herzog [ˇ黃鶴 ]ˇin Taiwan


Post Edited (Kramer) : 7/18/2006 3:22:34 PM GMT

Tom Walker
07-18-2006, 10:54 PM
I think that the implication was that the creation of PDFs need not be accomplished by Adobe software but instead by free, open-source software such as PDFWriter at sourceforge.

Adobe's writer is definitely not free...:)

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Truly Understand the Fundamentals and the Path will be so much easier...

matthelm
07-19-2006, 10:28 PM
Kramer said...
I will have to take another look, but I thought you had to get an Adobe licence for $$$ to create PDFs. Just the reading side is free.
Are you saying that everything is free?

...

Does OpenOffice handle both Chinese and English in the same text?

Sorry for coming down so hard on you, but Word (or OpenOffice) would be one of the worse formats to store any drawing in.ˇ The Fabrication and Assembly documents are DRAWINGS, not just text, so you do not want to store these in a bit mapped format. (as far as I know, Word (or OpenOffice for that matter)ˇonly supports bit mapped graphics)

Yes, there are lots of free PDF writers out on the market.ˇ They almost always install themself in Windows as print drivers.ˇ I use one called CutePDF.ˇ (mainly because it works with windows 64 (worse buy I've ever made))ˇ Also, most real CAD programs support printing to PDF, and the ones that don't, print to plotters, and there are lots ofˇplotter to PDF converters.ˇ The reason for this, is because cad programs store everything as lines with width, not a series of dots, which is also the way plotters and PDF stores things.ˇ That way, if you zoom in on a detail, you can SEE it, not a bunch of big dots.ˇˇ (yes, I know PDF can store bit maps too, but we don't want those either in a CAD drawing!)

I think the reason OpenOffice was brought up, was it supports direct saves to PDF, and the fact it is FREE!.ˇ I am not sure if OpenOffice handles what you wish to do, but it's a free download, so just download the latest version and give it a try!


Here is a link to a GOOD drawing in PDF format:
http://www.diodes.com/datasheets/ds30261.pdf
Zoom in on the data, and you still have good sharp lines.

Here is a link to a BAD drawing in PDF format (and what you'd get in Word):
http://www.micrel.com/_PDF/HBW/sy89854u.pdf
(last page, bottom view) Zoom in, and all you'll get is big dots!

It's kind of like using a print screen to save text files!!!

Loopy Byteloose
08-04-2006, 05:52 PM
Thanks.
I have given this a bit of thought and I have been stymied by a recent attempt to transmit Microsoft documents. They seem to be refused by a firewall or antivirus feature.

I am looking into using OpenOffice for converting Microsoft documents to PDFs.

The primary advantage is that the reader isn't usually able to modify the document, so glitches from accidental input are eliminated.

Also you have made it clear that the artwork isn't much more legible in OpenOffice.

My biggest problem is that I have to have two installations as I am still committed to the Microsoft Office in many ways. But this is certainly a better means of transmittal when changes may have a huge impact on outcome [such as the terms in a Purchase Order, etc.]

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"If you want more fiber, eat the package.ˇ Not enough?ˇ Eat the manual."ˇˇˇˇˇˇˇˇ


ˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇˇ Tropical regards,ˇˇˇˇˇ G. Herzog [ˇ黃鶴 ]ˇin Taiwan


Post Edited (Kramer) : 8/5/2006 12:17:53 PM GMT