Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


No Clean for BGA's

dragonslayr

#21801

No Clean for BGA's | 1 October, 2002

Just checked the archives with no real success so I am asking here.

Are there recommended no clean pastes for SMT reflow of BGA's?

Seems to me in recent threads a pro and con issue of whether or not to use no clean for BGA's is raised.

The BGA in question is a 196 ball, 14x14 grid, with 1.0mm pitch.

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eg

#21802

No Clean for BGA's | 1 October, 2002

Kester 256 has been v.good for us,

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#21807

No Clean for BGA's | 2 October, 2002

Dragon, Was recently responsible for No Clean Process/Material evaluation and implementation project. Shop was 100% Water soluble facility. Several Top Paste manufacturers were invited to participate. (3) were evaluated. All key variables were identified and measured in DOE. AIM NC 253 came out the winner. We had success with 14 mil. FP, 0603 resnets, .8 mm, 1200 I/O devices, CBGA, PBGA, column grid arrays, and micro's. Limited residues remaining, and less voiding characteristics. One key determination was the printing characteristics of the AIM. Having inline Cyber Sentries aided in measuring print conformance. Measuring relax and recovery times, clogging apertures, stencil life, etc. A 2% increase in yields was noted in ICT/FCT Test on the products/assemblies transferred to No Clean Process. Additional to the normal inspection/test gates we utilized a BGA Caltex Scope, and 3D X-ray (Tomosynthesis) to validate solder joint integrity, voiding, etc. Some of the bigger challenges occurred in Post and Touch up areas, and SRT BGA repair process. What kind of board finish is typical in your shop? If you'd like to know more of the specifics of eval., DOE outline, variables, and paste manufacturers give me a shout. Scott

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dragonslayr

#21810

No Clean for BGA's | 2 October, 2002

Scott - all sounds good. My primary concern is the residual flux left behind under the BGA. Will moisture entrapment become a concern over time? I believe that may be dependent on the flux formulation. I know that some no clean fluxes actually become a polymer resin when cured (something like a conformal coating) which I believe to be a good thing. I'm thinking that the right formulation would emulate encapsulation ala COB or die attach requirements. Am I on the right track here?

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#21884

No Clean for BGA's | 9 October, 2002

Kester 256 has also worked tremendously well for us. We have soldered thousands of BGAs from 156 balls to 780 balls .8mm pitch with no solder problems (shorts,opens or voids) and no residue problems. Give it a try.

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