Thanks Tom, very good.

All European schools and universities teach metric and that includes UK schools.  I was schooled in metric before starting my first job at a PCB fabricator where we received from customers, eighty percent of the time, thou (what you Americans would call "mil") for artworks and gerber data output from customer's PCB CAD systems, and a metric drawing for board dimensions and drill sizes that had been drawn up in a mechanical CAD system.  The other ten percent were predominantly all metric from European and Japanese companies.

To be honest it didn't matter one jolt to us as a fabricator what the customer supplied as the very expensive CAM software dealt with it well and it wasn't too difficult to convert between the two in your head after a couple of weeks.

In my  next job for Toshiba I used metric everywhere and also since.  It's not too difficult to use metric figures of 2.54, 5.08 etc. though with a grid step-size of 0.01 for feature sizes.

The fabricators I use nowadays all work in metric predominantly but again are happy to receive any data metric or imperial and happy to speak to customers in both systems.

On slides 26 and 27:

The only way to tell the difference between an imperial padstack in thou and a metric padstack in millimetres appears to be the person's common sense when looking at the numbers.  Oh dear.  In my experience common-sense can be sometimes lacking - and I certainly include myself sometimes in this category!

Perhaps a "l" suffix at the end of the padstack name to indicate imperial values (i.e.  ludite?) ;-)

On slides 33 and 34 the padstack name column seems to show some metric padstack names?

I use the IPC naming for landpatterns using metric sizes, i.e. 3216, 2012, 1608.  Again it's not too difficult to memorise both sets of metric and imperial sizes.  For an attribute for a part, where it appears on a BOM report though I use both sizes and am specific about which is which, for example: "EIA 1206, Metric 3212".

On mounting holes I created a number of non-part specific footprints in a library that can be reused that was based upon the screw and boss being used by the mechanical engineer so that we could work together and re-use successful boss/screw combinations and keep the number of screw/washer hardware parts to a minimum whilst I have a footprint that can be reused that includes relevant keep-out areas for washer/screw hardware and plastic boss on the bottom side of the board.  E.g.:

PCBMOUNT_H320_SCRW550_BOSS600-PLASTIC
Hole size is 3.2 mm, screw diameter is 5.5 mm, boss underneath is 6 mm, plastic.

I did start my own padstack naming convention here at Crowcon but when I saw you'd created one I changed my library over to use that instead as a single IPC standard that everyone should be encouraged to use is going to be better in the long run than anything else, and the sooner its adopted the easier it'll be.

Mine, also metric based, went like this:

<SHAPE><PAD WIDTH>X<PAD LENGTH>P<DRILL_SIZE>-<DRILL TYPE>

<SHAPE>
BULLET Bullet
DOGBONERECT Dog-bone
OCT Octagon
OVAL	Oval
RECT	Rectangle
RND	Round
RNDRECT	Rectangle with rounded corners
RNDSQR	Square with rounded corners
SQR	Square
TP	Test Point (round)
TPS	Test Point (square)
VIA-MICROVIA	Via (laser drilled micro-via)
VIA	Via (drilled)

e.g.

RND200P140D-PTH being a round pad 2 mm with a 1.4 mm plated drill
RECT130X350P being a rectangle 1.3 mm x 3.5 mm

I ended up finding your pad stack naming convention a bit more versatile with the exclusions and modifiers you'd created, in that I could name pads more specifically such as:

r1135_780r50h305o160xc340zc340

This is a rounded rectangle pad on the top layer with a round pad through the hole, and drill, suitable for the thermal tab of a TO-220 transistor which can be done with a single pad in Pulsonix and named easily with your standard, which I hope I've interpreted correctly - thanks.

Regards,

James

James Head BEng CID+ MIIE MIET
Senior PCB CAD Engineer
Crowcon Detection Instruments Limited
2 Blacklands Way
Abingdon Business Park
ABINGDON
OX14 1DY
Telephone: 01235 557700 extension 289
Fax: 07092024504
E-mail: [log in to unmask]


-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Tom Hausherr
Sent: 19 March 2012 16:52
To: [log in to unmask]
Subject: [DC] IPC APEX Designer's Day

Hi Everyone, 

 

I posted my IPC APEX "Designers Day" Power Point presentation on "PCB Design Optimization Starts in the CAD Library" here - http://www.pcblibraries.com/Forum/ipc-apex-expo-2012_topic6.html

 

This presentation contains recommendations for adding PCB library drafting elements such as Silkscreen and Assembly Outlines, Polarity marking, Reference Designator sizes, Local Fiducials, round-off resolution update and the implementation of Mil Units for the upcoming IPC-7351C standard. 

 

One note on the Mil Unit subject. As PCB Designers, we have been taught DFM (Design For Manufacturing) rules during our entire career. For the past 10 years I have been all over the world promoting PCB Designers to transition to the metric measurement system and revealing why the metric system is superior for PCB design layout. However, our PCB fabrication shops prefer Mil unit Gerber or ODB++ data, drill data, fabrication drawings and layer stack-ups, panel sizes, material thicknesses, etc. The global electronics industry including component manufacturer's, CAD vendors, fabrication, assembly, mechanical and PCB design is split down the middle on this subject. I believe it will remain this way until the PCB fabrication process completely transitions to metric. 

 

I've been on the open market contracting PCB layout for DOD companies and they're ALL doing mil unit PCB design. Most PCB design service bureaus are doing mil (inch) based PCB layout because that's what their customers are asking for. I've submitted employment resumes to firms all over the USA to seek employment and the vast majority of them are doing mil unit PCB layout.
At this year's IPC APEX conference there was a large crowd at the Designer's Day event and when I asked the question "How many of you are doing metric PCB layout?" only a couple people raised their hand. When I asked "How many of you are doing PCB layout in mil units?" the vast majority of the attendees raised their hands. When I asked people why they still do PCB layout in mil units the majority say "because our fabrication shops prefer mil units and we are big on Design For Manufacturing (DFM)". 

 

Most people in our industry refer to chip capacitors and resistors after their inch based names 1206, 0805, 0603, 0402 and not the IPC metric names 3216, 2012, 1608, 1005. All CAD vendors create their default software installation in mil or inch units (not metric). Popular PCB fabrication shops default to mil unit presentations in their private seminars to their customers or at IPC symposiums. Are we being brainwashed or are we in a state of chaos? 

 

I applaud IPC, JEDEC, NIST and the component manufacturing industry for fully transitioning to the metric unit system, but I fear that things are more messed up than ever before in our industry. Being split into two measurement systems is not exactly optimizing the electronics industry. So I propose that IPC go back and add mil dimensions in all of their standards to eliminate the confusion in dealing with dual measurement systems. IPC needs to recognize that a vast majority of the PCB industry is not transitioning to the metric unit system and that we need standards that are applicable to our profession today. Download my Power Point presentation from "Designer's Day" and you'll get a good taste of the metric / mil state of the PCB library industry. 

 

That's my opinion, what's yours?

 

Best Regards,

Tom

 

Tom Hausherr 

President 

PCB Libraries, Inc. 

13730 Sorbonne Court 

San Diego, CA 92128 

858.592.4826 Office 

858.859.5371 Cell 

[log in to unmask] 

 

 



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