Footprints / Land Patterns - Zero Component Orientation for undefined types

Zero Component Orientation for undefined types

Printed From: PCB Libraries Forum
Category: Libraries
Forum Name: Footprints / Land Patterns
Forum Description: [General or a CAD specific issues / discussions]
URL: https://www.PCBLibraries.com/forum/forum_posts.asp?TID=3027
Printed Date: 25 Nov 2024 at 9:20am

Topic: Zero Component Orientation for undefined types

Posted By: Chris M
Subject: Zero Component Orientation for undefined types
Date Posted: 28 Dec 2021 at 12:44am

I would like clarification of how to set the orientation of footprint types not defined in the standards. I have looked at examples from POD and they don't appear to match any convention.

1. Single in-line SMD, eg Kingbright LED APBDA3020. This is a 3 pin dual LED with three contacts on one edge of its ceramic base. I use the same convention as 2 pin devices like SMD resistors with the pads in a horizontal row with pin 1 on the left, but the POD footprint has pin 1 on the right.

2. Two row SMD connectors, eg board to board mezzanine connectors which come male/female or plug/socket. If you follow the IPC-7351B standard for two row ICs, eg SOIC, then pin 1 should be Upper Left. Because pin 1 swaps sides for plug and socket connectors one connector will have a horizontal orientation and the other vertical to keep pin 1 at Upper Left. For the Hirose BM10B series the POD footprint has pin 1 Upper Left for the plug and Lower Left for the socket which is inconsistent with the standard for ICs.

3. Single row SMD pin headers with staggered pads. Should these be considered single row (Horizontal with pin 1 at Left) or 2 row because the pads are staggered on each side of the centre line.If considered 2 row then their orientation will be horizontal for IPC-7351B (pin 1 Upper Left) and vertical for IEC 61188-7 (pin 1 Lower Left).

Or are there different rules for connectors and the IC rules don't apply?

Thanks for your help, Chris.

Replies:

Posted By: Tom H
Date Posted: 28 Dec 2021 at 10:11am

All unique through-hole and surface mount connectors use the mfr. recommended pattern.

We try to keep the pin 1 location to match the mfr. pattern.

The main fundamental aspect of the IEC Zero Orientation is to try to keep footprint patterns long in the X (horizontal) direction. Contributing factors are computer screens are longer in the X, most paper sizes are long in the X, PCB layouts are generally long in the X.

The original goal for establishing a Zero Component Orientation was to provide consistency to assembly shops to allow them to automate the assembly line. With no consistency, assembly shops must manually figure out the Zero Component Orientation for every customer. This process takes an average of 8 hours per PCB layout to setup the pick & place machines.

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Posted By: Chris M
Date Posted: 29 Dec 2021 at 7:56am

Hi Tom,

Thanks for your reply. Based on looking at the table of contents in the preview ofIEC 61188-7 which showed a section for connectors I purchased a copy. I was dissapointed that it did not clarify the situation for me.

I have decided there is no point in trying to interpret the standard for undefined types because it seems manufacturers have different interpretations (or they don't care and just show random orientation). Unless there is a guarantee that the assembly people will make the same interpretation I do they will still have to manually check connectors, etc. I have decided to just list which footprint types are Zero Component Orientation compliant on the assembly drawing.

I don't expect answers to these problems, but I will list them in the hope you have some influence on the committees or that someone who does reads this forum.

Pin 1. According to IEC 61188-7: The location of pin one in the land pattern or component description shall be identical with any polarization mark on the component. The Bivar SMTL4-RGB LEDs have the polarity marker on the pin 3 corner. What should you do? Break the IEC rule or change the pinout? Changing the pinout is dangerous if the schematic symbol designer matches the data sheet pinout and doesn't know you moved the pins on the land pattern.
Relying on manufacturer recommendations.

I don't ever recall seeing Level A or B being specified on a manufacturers datasheet land pattern drawing.
Some manufacturers don't specify pin 1 on connectors (eg Hirose BM10) so the footprint will be horizontal or vertical depending on where I choose pin 1. I don't know how standards can fix this, but it shows that the assembler cannot determine the relationship between the Zero Component Orientation and the tape orientation just from the data sheet. They could be loading the same connector from two customers and get two different orientations depending on where each customer placed pin 1.
The manufacturers can't agree. Cree and Kingbright both make RGB LEDs in a PLLC4 package. One shows pin 1 upper left, the other lower right. Who is right?

Despite what you said about the intention of the standard to orient components horizontally the IEC standard shows connectors being vertical for Level B (table 7).
Table 7 clearly shows that connectors follow the same rules as ICs - A top left, B bottom left and that they have to be rotated to conform to the pin 1 position. Plugs and sockets have mirrored pinouts so they should be rotated 90 degrees to each other to keep pin 1 in the correct corner. I haven't seen a manufacturer show their plug and socket footprint with different orientations.
Single in line devices, eg 3 terminal capacitor (a chip cap with GND pad between the two end terminal pads), an LED like the Kingbright APBD3020, a single row connector without assymetrical pads. These are not defined in IEC 61188-7 and the basic rules are confusing.

4.2 General basic rules last paragraph: components with more than two pins match the rules for Level A or B.
4.3 Level A basic rules: pin one shall be located at the upper-left or upper position. The concept of upper-left can't be applied to single row components so A specifies upper. This implies vertical orientation with pin 1 at the top. This is in conflict with the General basic rule: The component orientation shall position pin one as being on the left-hand side of the component description.
Now consider if the single row connector has optional mounting feet on one side. Without feet the Level A land pattern specifies pin 1 at the top (see above). When you add the optional mounting feet it looks like the connector in table 7 and level A is horizontal. It doesn't make sense for the same connector to have different orientation depending on whether the optional feet are fitted.

Kingbright APBDA3020 three pin LED. The manufacturer's data sheet shows pin 3 on the left and your footprint copies this. This is not compliant with any interpretation of the standard I can make. It looks to me as if the MCAD drawing was made without consideration of orientation and then the land pattern was drawn to match.

It doesn't matter if I got all this wrong., because if I got it wrong some one else will and the PCB orientations and the assemblers expectations will be different. To achieve the goal of Zero Component Orientation, ie accurate transfer of orientation to the the assembly machine, the standards need to cover these ambiguous or undefined types.