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The Knowledge and Know-how Connection
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June 17, 2013
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Which of these factors is more critical to the solder printing process, solder paste volume or solder print alignment?
Board Talk is presented by ITM ConsultingVisit ITM Consulting to learn more.Phil Zarrow, ITM ConsultingWith over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes. Jim Hall, ITM ConsultingA Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.
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Views: 2551
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Proper solder paste brick placement depends on proper stencil to board alignment, board pattern accuracy and stencil aperture location accuracy. See: http://www.lpkfusa.com/SMTStencil/whitepapers/index.html
If you do not place the solder brick in the right spot you may get incomplete joints, solder balls, or even shorts. And remember that lead free solders do not wick or creep as well as the leaded solders, which means you more likely end up with incomplete joints or even bare copper, depending on the surface finish.
If the solder brick is placed in the proper location, but an unpredictable and insufficient amount of solder was released from the stencil the result may be incomplete solder joints or misaligned components. The cause for this is typically related to an area ratio that is too small, poor aperture wall surface or a poor choice of stencil material.
Ahne Oosterhof, Eastwood Consulting, Hillsboro, OR USA
Gentlemen,
It is always interesting listening to your board talks.
As above subject is known to be "the yield" parameter of most importance for the bottom line result of any printed circuit assembly process, my curiosity was called for.
I do agree on all of your general comparisons and I'm fully aware that these Board Talks mainly are aiming at "the proper focus of any process". In that sense I'd like to add some comments.
First, the parameters of importance have to be isolated from each other to describe the influence of the others, one at a time.
Theoretically three axes symmetry for the final paste deposit is of huge importance, as the following reflow implements a number of forces, that influences the final position of any component, some more, some less, depending on physical size and footprint of the components - see below.
Component - When judging influence of volume / alignment it will always be done "thru observing the mounted components", which leads to an important parameter for the components invoked: The quality of components in the sense that they are supposed to be ideal with respect to footprint symmetry and wettability (yes I do know that its imaginary).
Volume - Volume @ 100% perfectly aligned: Mainly affects mechanical behavior - product quality
Alignment - Alignment @ 100% correctly dosed volume: Mainly affects bottom line - in the sense that 100% yield after reflow (which of course is a city out in No-where) reflects the lowest possible production cost (on that specific process).
And yes production of printed circuit assemblies is still achieved thru a number of compromises, which again is different from production setup to production setup.
Hoping that my way of thinking can inspire somebody to a yield full compromise:-)
Med Venlig Hilsen / Kind Regards.
Torben Norlyk, Integrated Defense and Security Systems