The importance of Cpk
ruining not only the print but the and more delicate and module layup is Achieving repeatable accuracy—and the
entire cell. Given the fact that printing is automated, the mechanical alignment high C
pk
values that reflect this—requires
the last process in the cell manufacturing systems that have until now been perfectly a wealth of experience in process control
cycle, this can prove incredibly expensive. adequate for PV manufacture will and design.
High C
pk
values are also fundamentally necessarily give way to the sort of vision-
important for selective emitter cells, assisted alignment techniques that have
another high-efficiency solution that is served the demanding semiconductor
Darren Brown is the business
currently the focus of much developmental industry so well for years.
development manager for DEK Solar.
work and which is expected to become Another critical issue is machine
commercially available later this year. This stability. Printing systems are typically
involves the use of preprinted fiducials equipped with large mechanical parts, such
to ensure the alignment of multiple print as work tables, print heads and handling
patterns on a PV cell to within just 10-12 systems that may go through extensive
µm of each other. linear or rotational excursions, thousands
A further way to increase efficiency is of times a day, at the 3-second beat rate
to move the relatively wide bus bars from that is the solar industry’s standard. As we
the front of the cell to the rear, connecting go forward with new developments like
them to the collection grid by means of those described here, speeds will increase
metal wrap-through holes, solar’s version and repeated alignment to within just a
of plated through holes, which again few microns will become the norm. As this
requires high C
pk
print processes. happens, it is essential that such masses
From the above it is clear that and their movements are minimised as
repeatable accuracy—and therefore C
pk
they may cause the machine to vibrate
values approaching 2—are soon to become during printing, compromising print
extremely important for manufacturers of accuracy and quality, or equally damaging,
solar cells and modules. We need only to they can over time progressively knock
consider that as wafers become thinner print alignment accuracies out of true.
14 – Global Solar Technology – July/August 2009
www.globalsolartechnology.com
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