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SMT Placment Reliability



SMT Placment Reliability | 4 May, 2000

There is a hypotheses floating here that the more surface mount components on a PCB, the percent of missplacments goes up. I'm on the receiving end of this, and looking for backup, or argument for the idea.

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Re: SMT Placment Reliability | 4 May, 2000

A Machines reliability will remain the same If it places 25 parts or 25,000 parts. It has nothing to do with "how many parts" but on the repeatability of the machine type. You would notice less misplacements on a low count PBC due to seeing less components on the PCB.


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Re: SMT Placment Reliability | 5 May, 2000

The placement defect rate also depends on the shape of the components. 0402's have a higher defect rate than 0805's for example. If the board is very dense populated, chances are that a misplaced part knocks off another part and all of the sudden there are two defects instead of one. I would hold on to your theory, but I think there is no proof to back it up. Stefan

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Re: SMT Placment Reliability | 5 May, 2000

Charles, This theory normally occurs when the machines being used have a CAM style pick-up mechanism( ex. FUJI-CP series). One of the many things that determine cam speed is how many parts out of a single feeder will be picked( It has to build up speed ). Once you go over the amount at which the cam speed reaches it's maximum velocity, I would agree that you will be more prone to pick up problems. This is normally the end result of improper maintanance but that is another issue. If you do not use machines that operate this way I would fight the theory and ask for proof.

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

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Re: SMT Placment Reliability | 5 May, 2000

Charles, The percentage of misplaced components can increase with the number of components, because as you increase the number of placements the travel of the PCB,for a fixed turret machine, increases in table speed and distance. The slower the travel for the table...the more accurate the placement. This would be questioned by the equipment manufacturers, but we all know that every pick and place machine has it's flaws. As for mobile head equipment, the quality of those individuals maintaining and calibrating the machines can impact the accuracy substantially. Look at the mechanical aspect first and go from there. I wish you luck, TNT

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Re: SMT Placment Reliability | 6 May, 2000

Charles: I don't know about machines doing what you're talking about, but I sure I know that I do!!!! Good luck. Dave F

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Re: SMT Placment Reliability | 8 May, 2000

Charles, I think the misplacement can be devided into 2 groups: 1. parts misplaced by machine 2. parts move as the X-Y table moves If you use the solder paster right, and the place force is properly setup, the second group will be definitely no except your machine has some problems like the board clamps are not stable. The first group is the realy misplacement rely on the CP/CPK your machine, it goes up as the SMT component increase, I believe that since it's random.

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