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pick and place for SMT components?

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sapphire_2010

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Hi All,

For any SMD component where should a pick and place point & why? Is the SMT machine automatically detect the pick & place of a component or we have to program that machine to pick component from a certain point? I define pick & place for a SMD vol regulator ( Its DD pak 3-leaded) at pin1 but SMT machine can't picks it correctly. Currently using Altium PCAD2006 software for PCB design

thanks
SA
 

The point you pick for the pick and place origin is generaly the centroid of the component. What ever point you pick generaly should be a flat area as most pick and place machines use vacuum heads to pick up the parts.
The reason the centroid of the component is used is to balance the component during the pick and place operation.
The attached to shows the pick and place origin as the red cross, VERY IMPORTANT that this location is the placement origin for the component.
 

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thanks Marce, for sharing this information. I will move the pick & place to center of package/footprint
 

Its what were here for, PCB design is hard enough these days and not taken as seriously as it should be as an engineering discipline.:grin:
When I started we drifted into from some field of electronics, were given a box of pretty coloured tapes, a scalpel and told to get on with it.
 

Have you still got your tapes though? :lol:

I usually struggle to find the exact point for the centroid on something like this as it is not at the mid point between the 2 smaller pads and the larger one
but more central to the larger pad.

How do you choose the centre on these Marce?
 

Trial and error most of the time, and working closely with the production department. Also using 3D software and a model of the part, you can then get the centre of gravity from the model, this then gives you the x,y point for the device. This method works well, but where you can liase with production because there are so many different heads, vacuum pressure etc etc
 

Marce
sometimes software's having capability to generate the centroid of component even though you have not specified while creating footprint.

In past , I have used Cadstar which was having this feature.

Agree with you,it's always better to specified centroid while creating footprint itself
 

For Cadstar I use footprints that follow the IPC-7351 format, wich I forgot to mention. All my footprints are done using the IPC calculator and in the past the PCBlibraries Wizard. This covers the basic packages, but some newer more exotic packages are appearing, especially where power is involved, a couple of diode packages have appeared, that are like the TO's but with only two pads, a J lead at one end and a large thermal pad at the other!
I also didn't mention, I have also played about with the shape of solder paste deposit for these types of components, to help balance the forces during reflow to minimise component skew as the solder liquifies.
 

is this Pick and place data from PCB tool is acritical one? Now a days the PAB assembly unit is not demanding the pick and place data if we are providing a gerber set to them . I think they are able to generate all required data from the gerber set.

Still no doubt it will be great if we can provide Pick and place point in the exact centre of component body. Some tools like cadence allegro is able to generate a placement file with body centre as the origin.
 

I have always created a pick and place file orin recent years provided ODB++ data. Gerber data is not intelligent so requires extra processing to create the required placement data.
How do you indicate your preffered 0,0 location or FID.
 

Yes, you are right Marce..now a days assembly unit demads ODB++ data.
But still in olden days ( recent past) they were able to place the component even though iI did not provide the pick and place data. I dont know how they managed to place the component. i think they may put some additional effort for this. They may be deriving the required data from the fiducials. But Iam sure very rarely they demanded pick and place data.
 

Most software packages allow you to create component reports with x,y and theta data, which gives you your pick and place data.
You can generate the data from gerber files but it is a pain as you have to reverse engineer the data somewhat, I have done it on peoples archive data, when they need a new board and only have gerber data to work with. it is quite labour intensive, and more prone to errors, especially for component rotations. Most good gerber front end software can determine packages from the pad flashes and you can also teachthem new package, so you scan the gerber data and get package placement, you then have to get the centroid data, edit any missed packages, assign a reference designator, and usually a part number or BOM reference...
Thats why I prefer my own controlled data:)
 

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