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Misplaced QFP240 component

Ramot Avichai


Misplaced QFP240 component | 17 May, 2000

I have shifts in the placement of qfp240 components. I have this problem with al my IC machines: Fuji-Ip2,Ip3 ,siemens F-4.

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Re: Misplaced QFP240 component | 17 May, 2000

Avichai: What kind of PCB are you using, when do you detect that shift (right after placement, before reflow, after reflow), does the shift always appear to be the same or do you see a variation, are you able to identify the process-step where it happens ?

just acouple of questions


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Bob P


Re: Misplaced QFP240 component | 17 May, 2000

If the shift is happening on different machines,it sounds to me like your pcba's cad data is incorrect or the board and/or fiducials are not consistent.

Good Luck Bob

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Re: Misplaced QFP240 component | 17 May, 2000

Ramot, Without further explanation everyone here is just taking stabs at it..... Sounds normal, I'm game! Have you looked at board finish(HASL?)?? Measured paste height?? Are they always off in the same direction? If not, Handling??

What are the specs for the part; size, pitch, weight, ect..??

That's just my opinion, I could be wrong!!!

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Socheat Khun


Re: Misplaced QFP240 component | 19 May, 2000

Hi Ramot; I have some sugestion for you, you may want to look at part data, like lead width, pitch , length.

Good Luck socheatk

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John McGriff


Re: Misplaced QFP240 component | 24 May, 2000

We just had a similar problem with misplacement, and it turned out that the designers had not put the local fiducials in the right places. I am told that placement machines typically recalculate the component centroid to be at the center of a line between the 2 local fiducials. Therefore, the fiducials must be exactly on a line through the corner of the part, and both must be the same distance from the part centroid. For a square part, this means on a 45 degree line through the centroid. Additionally, the local fiducials must be in the same place relative to the part for each occurence of the part (as adjusted for part rotation).


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Re: Misplaced QFP240 component | 24 May, 2000

John, Would you enlighten us to what machines you are talking about. I have never heard of such things. Typically, machines map out the boards with the locations of the fiducials relative to there CAD locations in order to account for stretch. Local fiducials minimize the amount of stretch that would be placed on the component in which they are localized to, for obvious reason! If you have true CAD for both the fiducials and the components, the only way to still place off, and have it be becuase of the fiducial locations, is to have the component lands and the fiducials in two different layers in your gerber files. Your board would be created by overlapping the layers! This is dealt with in the thread archives. I believe old Moon Man even hit on it a few time, but I could be mistaken. That's just my opinion, I could be wrong!

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