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Open v.s viscosity



Open v.s viscosity | 18 April, 2000

Hi, I got an interesting result after completing DOE that more open defects occurred higher the viscosity.The ppm would be 500 while the viscosity is 950 and it would be 1500 while the viscosity is 1050.The range of viscosity is 900 ~ 1100kcps. The paste supplier said the tolerance of viscosity meter is +/-50(Brookfield).I prefer to use lower viscosity paste(920~970).but it is difficult to supplier.They suggest to increase the flux content. but it may result in bridging. Could anyone give me some suggestions?

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Re: Open v.s viscosity | 19 April, 2000

Wister: Those are neat results!!!

What results do you get if you use different squeegee speeds with your viscosity DOE? With high viscosity and the print speed you're using the roll may be "skipping over" the apertures.

Wadda loose? Dave F

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Re: Open v.s viscosity | 20 April, 2000

Hi,Dave The "skip" wouldn't happened because we monitor the solder paste height every two hours.The open position is between chip terminal and the solder terminal lift a little not as same as tombstone.I suspect the activity of solder paste is a bit low when the viscosity is higher than its center value.if it means the activity of this paste is sensible? Rgs, Wister

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Re: Open v.s viscosity | 20 April, 2000

Wister: Oooo, I understand now what you mean by "an open." Sorry, I was (am) a bit dense.

Your hypothesis is reasonable. On the other hand, have you looked at the traditional causes of tomb stoning also? For a defect to be a "tomb stone," it doesn�t necessarily have to snap to the vertical. Those marvelous purveyors of drivel that write articles in the trade press like to make-up names for everything. They�d call this "draw-bridging". Consider: � Check reflow profile � Pads per SM-782 � Reduce amount of solder paste � Check component solderability � Place component accurately

There�s more in the archives, since it seems to be one of the topics that people like to drone on about. Here I am droning on about it!!!

Good luck Dave F

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