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Zero orientation, still puzzeling to me

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Category: General
Forum Name: General Discussion
Forum Description: general topics not related to other forums
URL: https://www.PCBLibraries.com/forum/forum_posts.asp?TID=846
Printed Date: 22 Nov 2024 at 5:20am


Topic: Zero orientation, still puzzeling to me
Posted By: Maarten Verhage
Subject: Zero orientation, still puzzeling to me
Date Posted: 07 Feb 2013 at 4:38am
Hi Tom,

Regarding component zero orientations something is still unclear to me. I can’t figure out how everything fits in to have the pick&place machines to do the right thing.

I make every footprint with FPX, so polarized capacitors have the positive terminal located left and this is pin 1. Cathodes of diodes are left and pin 1 as well and ICs pin 1 lower left. So this is my zero orientation right? The CAD program allows to rotate a component and this rotation value ends up in a column of the pick&place file. But not everybody makes the footprint according to the IPC guidelines. Still an assembly facility is able to do it right. Assume an IC footprint is created with pin 1 upper left then that is the zero orientation, right? Which is different compared to the lower left variant. Then I assume assembly facilities ignore rotation columns of pick&place files and determine the location of pin 1 themselves and give it a rotation value based on their own zero orientation standard.

I am actually amazed why it seems something like this is nowhere explained. I contacted an assembly facility to learn how they are working regarding the component orientation. They couldn’t tell me more than “The ODB++ files contains all the information”!! How frustrating is that.

My primary objective is not to learn everything about pick&place machines but basically what specific data in which file is used to drive those machines.

Could you please explain more about this?

I assume an assembly layer feature (like a 45° stroke) at pin 1 is seldom used by assembly facilities to determine the orientation right? Which assembly layer data is commonly used for assembly?

Silkscreen pin 1 location markers are commonly used for orientation for testing and manual board rework things, right and not in the assembly process, right?

Do you have any hinds for me to discriminate between a good and a bad assembly facility? What is the most professional way of working? For example whether they prefer ODB++ files or pick&place files.

Best regards,
Maarten Verhage


Replies:
Posted By: Tom H
Date Posted: 07 Feb 2013 at 9:12am
The average assembly shop spends up to 8 hours on each PCB design to figure out what rotation the PCB designer created the library in. They have to match the library Pin 1 location with the pick & place Pin 1 orientation.
 
IPC-7351C Level A = Pin 1 in Upper left
IPC-7351C Level B = Pin 1 in Lower left
 
The entire concept is simple. The PCB designer is supposed to use 1 of the 2 Zero Component Orientations throughout their entire library and never deviate from it.
 
Then a note on the assembly drawing is supposed to indicate which Zero Orientation the CAD library was built in, Level A or B.
 
Then the assembly shop has a known starting point to setup their pick & place line. The component manufacturer's place parts in the tape & reel in every rotation possible, but if the assembly shop knows the Pin 1 location & rotation they can easily match that up with each different component manufacturer's package rotations. This is a futuristic concept that one day the PCB designers and the component manufacturer's would have a cross reference table to standardize the location of Pin 1 for the sole purpose to automate the assembly process and eliminate the 8 hours of front end work.
 
The assembly process will never be automated until all PCB designers work in harmony together to adhere to a Zero Component Orientation and the component manufacturer provides tape & reel data that informs the machine what rotation was used in the component packaging.
 


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