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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Another SMT issue!about CSP

Bryan She

#28339

Another SMT issue!about CSP | 30 April, 2004

We tested J6 open on .5mm pitch CSP(In fact,only resistance much lower than normal).J6 is one of the corner ball of the CSP.Defect rate is about 3%. Stencil:4 mil thickness,10 mil square aperture, solder mask openning:10 mil diameter circle. Board finish of PCB:Imersion Ag. 8 pcs of such CSP parts on each board,fail happens on defferent Ref.des but only on J6 ball. Reflow oven:Vitronics XPM1240,prfile seems good. AOI post printing,and the result is good. Fails were found when runs the FT and Frequency test. Thanks in advance for your advice. Bryan

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Bryan She

#28340

Another SMT issue!about CSP | 30 April, 2004

Sorry,it's:the resistance is much higher than normal

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#28350

Another SMT issue!about CSP | 30 April, 2004

You're correct. Higher resistance with an open makes more sense.

Try running your profile on that J6, corner ball. There may be something in the board layout that is sucking the heat from that pad.

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Bryan She

#28357

Another SMT issue!about CSP | 30 April, 2004

Oh,the CSP outline is 5x5 mm,It's hard to attach such a thermal couple on J6 ball.Ok,I'll have a try.Thanks. In addition,I found that most of the balls are on some big copper sheets except the J1,J6 and J7 balls.defects happen only on J6. Thanks. Bryan

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Bryan She

#28358

Another SMT issue!about CSP | 30 April, 2004

Maybe some crack in the joints will cause such an higher resistance defects.I'll try some dye stain experiment.Thanks. Bryan

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#28362

Another SMT issue!about CSP | 1 May, 2004

You bet the cracks will give you high contact resistance.

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#28363

Another SMT issue!about CSP | 1 May, 2004

The large copper pours in the vacinity of this part make it essential that you get your thermal recipe correct. You may need to slow down your conveyor [decrease the ramp rates] in order to minimize the effect of the board has on the different heating and cooling rates of the pins of this device.

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