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PCB Expansion (Y & X-axis)

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#36824

PCB Expansion (Y & X-axis) | 25 September, 2005

Hi! I'm facing a strange problem where PCB expanded in X & Y-axis after bottom-side reflow. When the PCB send for Top-side printing process, it is abvious that the printing alignment on the PCB's pads are out.

With the problem mentioned above, I am facing multiple 0402 capacitor tombstoning.

Has anyone got any idea about how to solve this problem?

Note: nothing changed to the process, the problem come out of sudden.

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#36833

PCB Expansion (Y & X-axis) | 26 September, 2005

Not that this actually happens anymore, but could it possibly be moisture in the PCB? Have you tried baking one or two for a couple of hours then run to see if it repeats?

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#36834

PCB Expansion (Y & X-axis) | 26 September, 2005

Make sure the stencil lined up perfectly in the middle all along the width of the board. Everytime someone has told me that a stencil doesn't match the board, they were not critical enough on alignment. Usually they would say one corner is perfect but the other side was not. When I checked the "perfect" corner had a minute amount of skew.

Try printing some top sides before reflowing the bottom.

Have you measured the board before and after? What kind of percentage are we talking about?

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#36837

PCB Expansion (Y & X-axis) | 26 September, 2005

duplicate post, sorry

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#36839

PCB Expansion (Y & X-axis) | 26 September, 2005

"Note: nothing changed to the process, the problem come out of sudden."

Did this happen with a batch of boards you'd been running a while, or was it a new batch (lot/date code)of boards?

I'd be inclined to suggest that the environment that your mylar films are stored in at your board fab shop may be poorly controlled.

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