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December, 2011 Rewriting the Rules of Solder Printing By the Staff of DEK and Hansatech EMS Ltd.
been providing manufacturing solu- tions to electronics companies for over 25 years, during which time it has developed a very particular — and highly successful — approach to serving its marketplace. Rather than specializing in spe-
B
cific products or sectors as many of its competitors do, Hansatech develops solutions for problems common to many throughout the electronics industry. “We are consciously active in many different market sectors, pro- viding complex PCBs and full box- build services to companies in areas as diverse as aerospace, telecoms, industrial and medical. Our clients, who include many blue-chip compa- nies, all have their own specific sensi- tivities, and it is our job to understand what these are and provide for them accordingly, while getting their prod- ucts up and running off the produc- tion lines,” explains Paul Gill, the company’s managing director. One of the EMS provider’s great
strengths lies in its RF technology skills, and in fact, says Gill, this, or machine-to-machine
communica-
tions, is a common theme across many of its client sectors. Here, the electronics manufacturing industry is coming up against some major technology barriers, not least of which is the emergence of heteroge- neous, high density boards. This is where the electronics designer’s dream becomes the board manufac- turer’s worst nightmare, as DEK’s President Michael Brianda explains:
ased on the UK’s south coast, high-profile EMS company Hansatech EMS Limited has
“This sort of board, which is already common in mobile communications, medical and automotive products, will typically have tiny passive
SMT components can be
so tiny that simply exhaling can blow them off the PCB.
devices, ultra fine-pitch semiconduc- tors and larger components like USBs, sockets and displays, all of which are integrated onto a single densely-packed PCB”.
A Daunting Challenge Steve Deighton, Hansatech’s
Surface Mount Manager, is no
stranger to the issues such boards present. Hansatech is accustomed to making complex products — in fact,
the company is brilliant at making them. But when Steve first saw Hansatech’s latest challenge — a high-density product incorporating several very fine pitch BGAs placed right next to a huge QFP with a ground plane of the same dimensions, he knew that the sol- der paste printing ante had just been raised to an entirely new level. While the QFP called for a large volume of paste, the BGAs would, of course, only work reli- ably if their solder balls were tiny, well-defined, and absolutely distinct from each other. “The two component types were com- pletely incompatible with each other,” he recalls — exacerbated by the fact that the QFP “stood off” from the board without com- ing into contact with it. This design meant that Hansatech had to lay down even more solder paste under the device to bridge the gap. An EMS provider’s nightmare indeed. In looking for ways to make
this product efficiently and cost effectively, Steve found himself hard up against the physical laws
governing stencil aperture ratios and paste rheology — the smallest that print apertures can be for a given stencil thickness. If they are too small, the aperture walls themselves will end up presenting a large and sticky surface to which the solder paste will adhere, instead of printing cleanly onto the board. Given these limitations, Steve knew that in order to achieve the fine pitches demanded by the BGAs, he had to use a very
fine “4 thou” stencil, printing very precisely to deposit minimal amounts of solder paste onto the board. “The problem was that the same stencil was simply too thin for the QFP, so we were unable to bridge the gap”. Thus Hansatech had to add further paste to the ground plane on the QFP in an offline manual soldering process. Far from ideal, this solution, the only one then available, was expensive and time-consuming, and, as is inherent in any manual process, it was also inconsistent. “After the first few boards, the quantity of sol- der being deposited would inevitably wander,” says Steve.
Strong in RF technology
skills, this EMS supplier is coming up against some
major technology barriers with new customer designs.
DEK recognized very early on
that as many electronics manufac- turers started to evaluate their pro- duction processes for the emerging generations of electronics products — tiny 0.3mm CSPs and 01005 passives — standard printing processes would be stretched to their limits. DEK also realized that in order to provide the means to handle these tiny compo- nents alongside larger standard devices, it would have to redefine the rules governing printing and stencil aperture size.
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