Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Local Fiducials

Views: 3194

Can anyone tell me if they are aware of any pick and place m... - Oct 19, 2006 by Steve  

#44611

Local Fiducials | 19 October, 2006

Can anyone tell me if they are aware of any pick and place machines that can use 'randomly placed' local fiducials? Now, let me explain... Our machines (Contact 3S, and 3AV machines) can use local fiducials in several ways. We can use a single center fiducial in the center of the component, or opposite corners. The opposite corners is where I'm having my issue. Since we are a CM, our customers are laying out the PCBs. They are placing local fiducials in opposite corners on all quads <20mil. The problem is, they are not in the exact corners. One might be closer to the package land patterns than the one on the opposite side of the package. They are placed where the designer had room. I've been trying to tell our customer that these fids do us no good, as when you find the centers of the fids, and draw a line through them, the center of the line is not the center of the component. I generally get "Our other CM's never 'complain' about the way we place the fids." I'm not really complaining, I'd just like to be able to use the fids, as we get some slight positional variance on the big quads that gets much better when we use locals. So, my original question still stands. Are there machines out there that can use these randomly placed fids, or are they useless to everyone, not just me and my CS machines? Thanks in advance! -Steve

reply »

curious

#44612

Local Fiducials | 19 October, 2006

Maybe I'm missing something here (we don't use locals and have never found them to be helpful, Panasonic and Fuji) but the fid coordinates don't necessarily have to be the same position in relation to the part placed. If you can use global fids. (which obviously won't be the exact distance from each part), why would the local fids be any different?

reply »

#44613

Local Fiducials | 19 October, 2006

have not given much thought on this i use old amistar machines as far as i know the fids are just referances to where the part is i dont think they would have to be centered up with the part as long as they are in the same place from board to board.

reply »

#44614

Local Fiducials | 19 October, 2006

While I can only speak for Samsung equipment I believe that this would not be a problem for most modern machines as the local fid positions are usually programmable

reply »

SWAG

#44616

Local Fiducials | 19 October, 2006

We use random local fids on our Universal equipment - (they don't create a centerline placement point).

On your equip., maybe you could try to shoot/dive-bomb the QFP(s) all by themselves using the 2 "random" local fids as your baseline reference points? In other words, shoot all parts on the board relative to globals. Start over with this process and shoot the QFP's all by themselves with reference to the locals. I suppose this might ensure that the QFP's are being aligned with the locals as long as they are assigned with the QFP's only in the program. You really need the exact/gerber location of all fids if you consider them to be random or non-symetrical. Sometimes we take short cuts and shoot locals fids in relation to globals and get some twisting going on with fine pitch stuff. We then put small rotations on the QFP to get it dialed in. If you have the gerber locations of these fids, you shouldn't have to do that. Just a thought - I might be full of it.

reply »

#44617

Local Fiducials | 19 October, 2006

Something that I find unusual in some of the replies is the fact that local fids that are randomly dropped around the quad don't do anything for assisting the alignment of said quad. The only way that I am aware of the local fids being useful is if they somehow correspond to the exact center of the part, either by being in the center, or by having the corner fids in the exact opposite corners.

Our machines are certainly able to place the quads without the local fids, based on only globals. The locals just add a bit of accuracy to the fine pitch parts. The only way to use locals on the CS machines is if a bisected line between corner fids falls in the exact center of the part. Not just close. We are talking 19mil here. The only other option is a center fid, again not just close, but the exact center. SWAG, If you have two corner fids on a board that you are populating with your Universal equipment, what does the machine actually do with the locations of the fids, if it doesn't draw a centerline? I do appreciate the input thus far. Thanks!

reply »

#44618

Local Fiducials | 19 October, 2006

Also, with our CS machines, I don't need to know the exact location of the fids, I just teach them to the machine. What the software does with the data is bisect the line the centerline between the fids to find the centerpoint of the part.

reply »

curious

#44619

Local Fiducials | 19 October, 2006

The fid is just a "known reference" location, the only advantage/difference is proximity to the part. It almost sounds like you are using the local fid as your part placement coordinates? So maybe the CS machine IS different but something doesn't sound right.

good luck and let us know what happens

reply »

curious

#44620

Local Fiducials | 19 October, 2006

OOps, to quick on the draw. If you have the CAD data for you fids I'll bet if you input those numbers (not teach on the machine) they'll work. Do you teach your globals the same way?

reply »

#44621

Local Fiducials | 19 October, 2006

We teach all of the fids. Globals and Locals. This is because we use a magnetic table, not a pass through conveyor. Without showing the machine the global fids, it has no idea where we've mounted the board.

reply »

SWAG

#44622

Local Fiducials | 19 October, 2006

Can't explain - I don't really know how it works mathematically.

reply »


RDR

#44623

Local Fiducials | 19 October, 2006

to use local fids such as this you must use the cad data, when the machine knows where it is supposed to be and seeks there it reads where it (PCB) really is and then corrects the machine, it does not have to be symetrical at all. If you teach fids on a skewed board you get skewed placements.

Russ

reply »

#44624

Local Fiducials | 19 October, 2006

Our machines can't use 'cad data' for fids. I'm intimately familiar with these machines as I've been using them for 11 years. Most likely, it's a limitation of our machines/software, whereby it requires symetrical local fids. When we place a PCB on the magnetic mounts, we show the machine where Zero and Skew fids are on the first board of the run. From that point it will seek out that location on subsequent boards and read the fids. Locals work slightly differently. We first teach (or import cad) the board. When we step through placements visually, we can 'enable' local fids on any of the placement. Once enabled, we show the machine where they are, since that can vary from one customer to another. As long as the bisected line falls dead center, the corner fids work fine. This has never been a problem with most customers. I just have one that drops the local fids 'where there is room'. That doesn't work for us. This sure is hard to explain. :)

Russ, The first step of our programming is to 'build the board'. This involves showing zero and skew. From that point on, all digitized parts take the skew into consideration. Teaching a board that is skewed does not result in skewed placements with this machine.

reply »

#44625

Local Fiducials | 19 October, 2006

Steve,

I believe Contact Systems is the only company that uses local fids in this way. All othe machine have coordinates for the local fids. When measuring the fids it applies any error from the fid measurement to the 1 component it's linked to.

Jerry

reply »

Base

#44629

Local Fiducials | 20 October, 2006

I know that on Philips Topaz equipment you can define the XY locations of the individual local fids relative to the mount-center of the component that they apply to. So if they are not symmetrical w.r.t. to the QFP's center there's no harm done. You only have to know the coordinates of the fids and the QFP and define XY of the local fids relative to the QFP in the program.

reply »

Base

#44630

Local Fiducials | 20 October, 2006

By the way: I've also used the corner pads as if they were locals. You can take a bitmap-picture of the pattern, store it and refer to it as a fiducial. Works great and you're sure they don't wander all over the place w.r.t. to the component's XY.

reply »

Phil

#44631

Local Fiducials | 20 October, 2006

The algorithm in our machines calculates the coordinate of the centre point between the local fiducials, compares it to the theoretical coodinate in the program data and applies any difference found as a "percentage" correction to all placement coodinates in the vicinity of the locals.It therefore dosn't matter where they are located.

reply »

#44633

Local Fiducials | 20 October, 2006

I really appreciate the input, guys. Having only had the opportunity to run the Contact machines, I was not aware that many of the other machines use coordinates for locals.

Now about those damn, mid-chip solder balls.... oh, that's another topic.

reply »

#44634

Local Fiducials | 20 October, 2006

Hi Steve- Not being familiar with CS machines as you are...but do you need to use fiducials for a 20mil QFP? If so...OK...just curious.

Also, it would be nice to know the reference point that the board designer uses... Board corner, Centroid, part corner, theroratical X,Y, who knows. How is he referencing local fiducials to the part

Would you be able to use pads? I know depending on the machines vision system and the space between pads....I know and heed warnings with using pads...but it just a suggestion.

Sounds like the old style machines you have follow the old school fiducial protocol found at http://www.smema.org/smema3.1.pdf

reply »

#44635

Local Fiducials | 20 October, 2006

nodlac, You are correct with the SMEMA3.1 document. Also, please note that I said I like to use local fids for <20mil, not for 20 mil pitch. The machine places the 20mil just fine, but there are occasions for whatever reason that we get some rotational inaccuracies on certain parts. Generally a properly placed (as far as my machine is concerned)local fid aids in the correction of this problem, by increasing the accuracy of the placement. I'd also like to mention that we couldn't be happier with our CS machines. One is 11 years old, and the other is 9 years old. They have nearly 100% up time, and do everything that we throw at them... even with some apparent fiducial limitations :)

reply »

#44636

Local Fiducials | 20 October, 2006

mid chip solder balls we had that trouble for awhile we went from a 8 mil thick stencil to 6 mil stencil and did some home plate style of cut outs in the stencil for the 1206 caps and resistors it seemed to fix our mid chip solder balls

reply »


RDR

#44640

Local Fiducials | 20 October, 2006

Gotcha Steve, so then in essence if you teach the skew, then the Machine "straightens" it out then right?

Russ

reply »

Six Sigma Training

vacuum tweezers - manual pcb assembly