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how to prenvent flux risidue in the blind vias.

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Eric D

#47664

how to prenvent flux risidue in the blind vias. | 15 February, 2007

one of my customer areworried about the flux risidue in the blind vias, or if the plug the vias and there is air trapped the plug will blow during our process. Appreciate for your response

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RDR

#47674

how to prenvent flux risidue in the blind vias. | 15 February, 2007

only plug one side, you can definitely blow out during reflow process with a sealed via/

it is impossible for flux to be trapped in a blind via.

Russ

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#47832

how to prenvent flux risidue in the blind vias. | 19 February, 2007

Russ

We agree with your comments on plugging from one side only. But...

We believe that it IS possible to trap process chemicals [technically, not flux] in a blind [or any other] via. This can be done by plating the via closed, rather than plugging or tenting, during board fabrication. The current used in the plating process tends to concentrate at the knee [corner] between the hole wall and the annular ring around the hole. This higher current density produces a thicker plating at that corner. This is called 'dogboning', or a 'dogbone'. [Not be confused with a "dog bone" pad/trace design that was often used in older BGA designs.] It can be observered by making sections of the via and by measuring the diameter of the hole after plating. Taken to its conclusion, the increased plating thickness will close the via opening, trapping plating fluid in the via.

References to dog boning in plating thickness are: * http://www.eiconnect.com/eiPcbRes.aspx?type=pcbterms

* http://www.copperplating.net/

* http://www.prc.gatech.edu/academics/elpkg/pdf/module7-sld.pdf

* http://www.finishing.com/4800-4999/4995.shtml

* http://www.finishing.com/98/22.shtml

* http://www.gold.org/discover/sci_indu/gold2003/pdf/s36a1243p870.pdf

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RDR

#47845

how to prenvent flux risidue in the blind vias. | 20 February, 2007

thank you very much Dave! I really appreciate the feedback. I brainlocked on soldering assembly process.

Russ

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