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SMT electronics assembly manufacturing forum.


SMT Component rotation problem

Chris

#23547

SMT Component rotation problem | 27 February, 2003

Hello, I am the manager of a Drafting department and don�t pretend to know too much about the SMT process. But I am the manager of a CAD designer so I am somewhat responsible for the following issue. So since no one else around here seems to have the time to address this, I�m going to take a stab at it. When our PCB design CAD system spits out surface mount component coordinates (location and rotation), a lot of times the rotation does not match that of our PnP equipment. So we run our CAD data thru a fixer-upper program that corrects the rotations, and then send it to PnP. So obviously my question is �what�s broken here?� From what I can tell, we�ve got three variables; the CAD data itself, the GF(?) file, and how the part is oriented in the tape. Which one of these is supposed to dictate rotation, and which of the other two must be modified to meet that rotation? From here in Drafting, it looks like changing the CAD data is out of the question because doing so would require modifying our core CAD cells with would immediately screw up all the layouts that they already reside on. Please someone clue me in. I hope all this makes sense. Thank You!

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RDR

#23548

SMT Component rotation problem | 27 February, 2003

Machine rotation is usually based off of component presentation. for example an SO8 can come in either tape and reel and sticks. In tape and reel the component is presented to the machine with pin one at the lower left corner while the stick will have it in the upper left corner the parts are 90 degrees different. Depending upon your cad library and machine library the rotations need to be the same. Your cad library shape must be the same as the PnP component lib. e.g. an SO8 should be layed out with pin one orientation the same as the PnP machine has it defined (maybe lower left, maybe not) SOT 23 packages are usually layed out from cad with the single pin pointing upwards for a rotation of 0 while the machine has it at 0 rotation for the single pin pointing to the left. So, to make them match either the machine OR the cad system needs to be the same. Both are an extreme amount of work depending on the size of librarys. using a system such as Uni-Cam can help but it still requires that each package/shape be gone through to change rotations to match machine library.

hope this helps

Russ

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genny

#23549

SMT Component rotation problem | 27 February, 2003

We have struggled with this as well. Basically, we have a consistent rotation for all packages of the same type, but I don't think our rotation has anything to do with the actual rotation that the PnP equipment actually wants to see. I believe our board stuffers mostly ignore our rotation information, or have figured out relative movements based on our rotations and what packaging we send the parts to them in, and do their own fix-it routine. My Question is: are parts in the same package type always oriented the same way in the tape and reel? ie. Are SOT-23 always the same way or are they some times 90 or 180 degrees different for different part values or manufacturers? Also, are 0603 or 0402 always the same way in the tape as well? I heard that sometimes they are rotated 90 degrees. I don't work in inventory, so haven't handled a lot of components and have wondered this. What if you have two different manufacturers approved and they orient their SOT's differently in the tape? Or what if sometimes you can get tape and reel, but sometimes all you can get are sticks for IC's. So many variables...

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RDR

#23555

SMT Component rotation problem | 27 February, 2003

Genny you are right on with the differences between suppliers/packaging etc... I am a CEM and you are correct that we pay no heed to cad rotations from our customers/designers. A.V.L./manufacturers P/Ns information specifies orientations and such. SOT23s are usually always the same but not always. DPACKs and such are always different it seems even if they are the same P/N and Manufacturer. Just to add a little more variable, some machines present parts from the rear of the machine wich requires a 180 deg. rotation from those on the front. So I guess to answer the original question, If you are an OEM that designs and builds the products internally you may have a chance at getting everything consistant. This can be done by always buy T&R for a certain P/N and never change or stick etc..., verify all component P/Ns have the correct AVL information regarding packaging and such, have your machine programmers match there component data with the CAD system or Vice Versa, etc...

Russ

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JAX

#23557

SMT Component rotation problem | 27 February, 2003

Cad rotation should not change with relation to how the part is presented to the machine. It should only depend on how the part is orientated on the PCB when the PCB is at 0 rotation. There is a seperate field to input part rotation inside a feeder. There are standards you can follow for part orientation, JEDEC has some. The problem you are experiencing is due to the orientation you define in your design software for every new package you come across. If you use the same guidelines for package rotation in your CAD software as you use on your machines.... everything works good. If your machine library is not setup to a standard then it doesn't really matter what you do, although I doubt this is the case since a rotation standard is common for smt pick&place machines. (At least all that I have worked on)

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#23558

SMT Component rotation problem | 27 February, 2003

Oh dear, I tried not to respond but i couldn't help myself. Stop me if I go off into the woods.

My guess, Chris, based on your fleeting reference to GF files, is that your SMT machines are Siemens Siplace. If this is so then package orientation definitions are limited by the fact that the long axis of the nozzles that are used to pick the parts are oriented along the x-axis of the package. To use the trusty SOT23 example this means that the single lead is usually defined pointing upwards when viewed in the Package Form editor - this defines the 0 degree orientation of the part. (The package could also be defined with the single lead down but that just complicates things - but it cannot be defined with single lead to left or right because that would cause pickup problems on the machine.) Continuing on, if the SOT23 is presented to the machine in tape where the single lead points left then that feeder must have a 90 degree pickup angle - if it points right then it must have a 270 degree pickup angle. This business with the nozzles tends to complicate the definitions of SOICs compared to TSSOP type packages. SOICs are typically defined with leads along top and bottom and pin one bottom left. But with TSSOPs the body "width" tends to be longer than the "length" leading the package being defined with the leads down left and right sides and pin on top left (or bottom right). This is confusing because SOIC and TSSOPS are essentially variations of the same thing.

I sense a lot of blank looks now so I'll stop and get back to my real job.

So, having said all that your current method, in the absence of a universal CAD translator or pixie dust, seems like a reasonable approach... you seem to understand your problem and are dealing with it in a sensible way. I'm sure there will be someone out there willing to sell you CimBridge, CamCAD, TIMMS etc.

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