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Rewriting the Rules of Solder Printing
At Hansatech, ProActiv is installed on-board DEK's Europa print platform.
By the Staff of DEK and Hansatech EMS Ltd.
Based on the UK's south coast, high-profile EMS company Hansatech EMS Limited has been providing manufacturing solutions 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 specific 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, providing 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 companies, all have their own specific sensitivities, and it is our job to understand what these are and provide for them accordingly, while getting their products up and running off the production 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 communications, 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 heterogeneous, high density boards. This is where the electronics designer's dream becomes the board manufacturer's worst nightmare, as DEK's President Michael Brianda explains: "This sort of board, which is already common in mobile communications, medical and automotive products, will typically have tiny passive devices, ultra fine-pitch semiconductors 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 solder 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 reliably if their solder balls were tiny, well-defined, and absolutely distinct from each other. "The two component types were completely incompatible with each other," he recalls — exacerbated by the fact that the QFP "stood off" from the board without coming 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 solder being deposited would inevitably wander," says Steve.
DEK recognized very early on that as many electronics manufacturers started to evaluate their production 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 components alongside larger standard devices, it would have to redefine the rules governing printing and stencil aperture size.
The breakthrough ProActiv process technology, which can be fitted onto all DEK printers, enables the industry's smallest components to be printed alongside its largest and most complex, using a conventional printing process and a single thickness stencil. It does this by energizing the paste that is in contact with or in very close proximity to the squeegee blade. This "shear thinning" process renders the paste more compliant so that it is ready to print immediately, and enhances the bond between the solder particles while increasing their density within the stencil apertures, providing manufacturers with better aperture fill.
The business end of ProActiv is special squeegee.
By making the paste more cohesive, ProActiv also facilitates its release onto the board rather than sticking to the aperture walls, improving print quality and paste release. All of these factors combine to allow electronics manufacturers to reduce aperture ratios considerably while increasing the thickness of the stencils they can use.
When he heard about ProActiv, Steve had no doubts whatsoever that this was the answer to his problems. "When I understood that we would be able to use a thicker stencil on our DEK Europa printer while reducing aperture sizes, I knew immediately that ProActiv was perfect for this specific board, allowing us to print everything in one online process, using one single-thickness stencil". Indeed, he was delighted to find that, by DEK designing the right aperture sizes in a 5 thou stencil, he was able to lay down enough solder paste for the QFP, while maintaining the control and precision work necessary to handle the tiny BGAs. All in one pass, in a drop-in process.
By using ProActiv, Hansatech has significantly cut the time needed to manufacture this board, while eliminating the expensive offline manual printing process — a result that is worth celebrating, as Steve explains: "This has given us greater control over the entire process, and as a direct consequence, our quality has improved — the print is flat and consistent, and the features are impressively well-defined, across the PCB, and throughout the print run — in fact, ProActiv has helped us manufacture some of the best-looking products we have seen".
As Hansatech's confidence in product quality grew, and Steve's team learned to trust the process, they were able to increase their cycle speeds, with excellent results: "Almost from the outset, our throughputs and efficiencies improved no end, so we benefited in terms of time and costs right from the start," he says.
Increased quality leads to better yields, less rework and a host of other benefits that go straight to the bottom line of any business. Another cost benefit has come in the shape of reduced stencil maintenance, as Steve points out: "It is clear, just from watching the squeegees, that ProActiv handles the paste very nicely. The paste is print-ready right from the start, and it just falls off the squeegee, so every sweep is clean — the stencils require less cleaning as the paste seems to move better, and paste release is much improved. Our manufacturing environment tends to be high mix and low volume so we never wear out our stencils, but given the way it works, it's easy to imagine that ProActiv could be instrumental in extending stencil life in a higher volume production environment," he says.
While ProActiv's many advantages have been so dramatically proven, there are some added benefits that are key to a forward-thinking EMS provider, as Steve underlines: "ProActiv gives Hansatech a significantly wider process window, and this is invaluable as it allows us to go out with confidence to our clients and take on much more difficult boards, extending our business offerings considerably."
So just as DEK is using ProActiv to rewrite the rules of electronics stencil printing, ProActiv is enabling electronics manufacturers all over the world to revolutionize their processes and rewrite their own rules about what they can achieve for their ever more complex and demanding industry. All of this with a drop-in technology that takes half a day to install. Simple, easy-to-use and a revolution in the making, ProActiv delivers unprecedented paste transfer efficiencies and a stable process that significantly increases quality, yield and throughput while reducing production costs substantially.
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