Solar Power International brought familiar names, faces and memories.

With the solar energy market expected to expand as rapidly in the upcoming decade as SMT did in the 1980s and ’90s, many parallels are being drawn between the two, and some familiar names and faces from electronics manufacturing are now appearing in the solar sector.   
Like at Solar Power International 2009, for instance. America’s largest solar energy conference and expo, SPI, was held at the Anaheim convention center in late October. With over 24,000 attendees and 900 exhibitors, the atmosphere was reminiscent of the Nepcon shows during the boom years of SMT.  

Recognized leaders in the SMT supply chain exhibiting at SPI included BTU, Flexlink, Datapaq, Christopher Associates, Henkel, Cookson and Hisco. These suppliers have identified applications for their core technologies in the photovoltaic (PV) market. Some have made minimal changes to current products, while others have developed new offerings tailored specifically to the demands of this emerging technology.

BTU (btu.com) has long been recognized as a leader in reflow processing for its high thermal transfer efficiency ovens. But before its first reflow oven was even designed, BTU was already serving the solar market. Atmospheric pressure chemical vapor deposition (APCVD) technology was developed in the 1980s to deposit anti-reflective coatings on glass panels. The process is still used today, and BTU’s lineup has expanded to include newer, more varied equipment that supports both silicon and thin-film PV technologies. With 50 to 60% of BTU’s business now in the solar sector, vice president of sales and marketing Jim Griffin suggests that in order to maintain a successful business position, “product diversity is an absolute necessity, and an organization must keep their presence global.” He credits his organization’s growth in solar to its ability to leverage its worldwide support infrastructure, which includes manufacturing facilities and applications labs in the US and Shanghai.  

Flexlink (flexlink.com), known to electronics manufacturers for its configurable conveyor systems, also provides material handling systems to solar assemblers. Photovoltaic panels are both heavy and delicate, so Flexlink combined expertise in moving delicate circuit boards and heavy, palletized industrial assemblies to design low-vibration, scalable solar panel handling systems. According to Michael Hilsey, Flexlink’s director of marketing and indirect sales, moving into this new market was a “natural progression,” which is why it claims the largest share of material handling systems in the solar manufacturing industry.

Datapaq (datapaq.com), providers of thermal data loggers for reflow characterization, now offers similar products designed for solar manufacturing processes. Some of the modifications to the reflow logging gear include protective shells that can protect the loggers at temperatures up to 800°C and withstand vacuum pressures equivalent to 300 lbs. of force. The six-channel systems run sample rates of up to 20 datapoints per second to monitor ramp rates as steep as 100°C per second. Now that’s hot.  

Christopher Associates (christopherweb.net), best known to assemblers for bringing the revolutionary Koh Young solder paste inspection systems to America, now offers a full lineup of solar manufacturing equipment and materials. Matt Holtzman, Christopher’s president, says he has applied the lessons learned through his 30 years of international circuit fabrication and assembly experience to the solar manufacturing world. Having witnessed the multiple booms, busts and consolidations in the circuits industry, he predicts similar movement in the solar manufacturing domain, and is prepared for them. His strategy: “to provide the inevitable differentiator in a developing market – service.” Christopher provides a full lineup of both equipment and materials, most of which are imported from Asian countries, which now lead the global value proposition in solar technology.

On the materials side of the market, Henkel (henkel.com/electronics) is identifying numerous crossover applications for its products typically used in electronics manufacturing. Similar to its functions in circuits, conductive adhesives replace solder in applications that will not accept solder (like glass, for example); silver flake filled epoxies work as grounding die attach materials; low-residue rosin-free fluxes are used in automated soldering equipment; thermal management materials are used to sink heat, and conformal coatings protect assemblies against harsh environments.   

Cookson (alphametals.com/products/photovoltaic) is capitalizing on its expertise in soldering materials to gear new products to the process demands of solar cell assembly. Designed specifically for tabbing and stringing operations, ultra-low solids liquid fluxes have been designed to minimize maintenance and activate very quickly, because soldering cycle times are incredibly fast – often less than two seconds. Addressing the process concern of flux overspray and its associated maintenance costs, Cookson has developed a dry flux that is applied directly to the solder ribbon. Dubbed “Ready Ribbon,” the solder-covered copper ribbon is pre-coated with a dry flux, which eliminates the need for spraying, and therefore, cleaning. Steve Cooper, Cookson director of global business development, said, “Since its introduction earlier this year, we’ve seen a significant interest, particularly from module manufacturers.”  

Hisco (hiscoinc.com/solar), known for its extensive distribution network in North America, is positioned to support all facets of PV assembly from module manufacturing through installation. Its end-to-end approach is based on distribution experience in the electronics market, and it couples extensive product offerings with service. Boasting over 100 certified professionals on staff, Tim Gearhart, manager of Hisco’s Silicon Valley branch, says, “Having experts who can help solar manufacturers optimize their processes is one of our greatest strengths.” Hisco’s website illustrates the broad range of photovoltaic technologies and the numerous areas supported by his organization.

It’s no surprise to see leaders in SMT assembly taking leadership positions in PV assembly, and it will be no surprise to see many followers tagging along as the industry prepares for explosive growth. What will separate the leaders from followers in the brave new world of solar manufacturing? The same characteristic that has differentiated them for years in the SMT world: customer focus. 

Chrys Shea is founder of Shea Engineering Services (sheaengineering.com); This email address is being protected from spambots. You need JavaScript enabled to view it..

Poor plating can be a culprit, and audits are in order.

This sample via hole (Figure 1) has been mounted in resin and microsectioned to look at the plating quality. The optical image clearly shows the resin surface at the back of the hole. This is a through-hole plating problem, and closer examination of the plating is required. The center of the sidewall may show the problem relates to the initial metallization process or the electroplated copper. The poor coverage in this example could have been caused by residues on the surface of the drilled hole that were removed during plating. Or, it could be related to a gas bubble in the hole during plating. In the case of less obvious examples, a light is put behind the microsection to show up the degree of laminate coverage.

Auditing the printed board fabrication process with samples examined from drilling through the final copper plating process should be considered. Optical examination of hole coverage and microsections should illustrate satisfactory process control.

These are typical defects shown in the National Physical Laboratory’s interactive assembly and soldering defects database. The database, available to this magazine’s readers, allows engineers to search and view countless defects and solutions, or to submit defects online

Dr. Davide Di Maio is with the National Physical Laboratory Industry and Innovation division (npl.co.uk); This email address is being protected from spambots. You need JavaScript enabled to view it.. His column appears monthly.

Main considerations for incorporating test in a board design.

In our experience, there is a general lack of awareness about what needs to happen at the design level to increase the testability and overall test coverage of a finished assembly. This issue is straining the customer/supplier relationship, because it goes beyond what the supplier independently can provide without customer input and consideration during design.

What is the basic problem? Suppliers spend millions of dollars and countless labor hours on different quality initiatives aimed at producing zero defects. Yet none has been able to achieve this without one certain element: test!

In design for testability, the test method must be decided prior to finalization of the design. The four main options are functional, in-circuit (ICT) fixture, flying probe ICT, and boundary scan. Each has different design considerations.

ICT with fixtures has been around the longest and is the most widely used. It is particularly well suited for high-volume, low complexity designs, where the (high) cost of fixturing is justified by the volumes. It can test for shorts, opens, capacitance, resistance, inductance and more, depending on the level of test desired. It is fast and cheap (at a price per test level, once the fixture cost has been absorbed). But fixture costs are high and not suited to low volume. Also, test pad sizes must be large (0.030˝ to 0.040˝) and contained on every net of the design to give the fixture access to the board. The large size of the test pads makes this option difficult to incorporate onto high-density designs or designs with BGAs. After all, the main point of going to BGA package styles is to save real estate. Adding large test pads on every net defeats the purpose.

Functional test also is widely used to “exercise” the end functionality of the board. Its intent is to test circuit functionality and, in theory, catch most major defects, be they component-level or manufacturing defects. However, this is not an opens and shorts test. For example, it would not typically reveal wrong values for passives.

Functional fixturing can be tailored to almost any application. It detects problems with the board functionality or component-level failures, depending on the test hardware and software design. The custom design of test hardware and software, by its very nature, makes this option time-consuming and expensive. For many applications, especially quickturn prototypes or products with short time-to-market, this may not be practical. Also, it is likely functional test will not cover as much as 20% of the circuitry, and thus leave vulnerabilities in the finished product. This is why many high-volume, high-reliability customers do both ICT and functional.

Flying probe, like standard ICT, will test for shorts, opens, capacitance, resistance, inductance, etc. But rather than using fixed test probes, it uses robotic test heads. The obvious advantage is greater access to the circuit board, for greater test coverage, without the high cost of fixtures. In addition, it allows a more “forgiving” DfT approach by enabling smaller test pads (0.010˝ to 0.012˝), enabling use of unmasked vias as a test pad, and enabling test of SMT and PTH component leads. In essence, almost all standard SMT or mixed technology boards can now be tested and with relatively high coverage ratios, even though they may not have been designed with ICT in mind. Also, since there are no hard fixtures, the upfront costs are substantially less. It does require custom software test programming, at a typical one-time charge of $1,000 to $2,500, depending on the number of components on the board and the number of different line items on the BoM. The biggest drawback is test speed. It can take five to 60 minutes to test each board, depending on complexity. It definitely is more suited to low- to medium-volume applications. The other drawback is it cannot test BGA pins without specific test pads on the nets leading into the device, and it cannot functionally test ICs or catch cold solder joints.

Boundary scan is one of the most interesting, most powerful and least understood test options. Incorporated into the original design, it allows the user to program and test many of the major devices on the board, including memory and FPGAs. In essence, it allows programming and functional testing of all JTAG-compliant devices purely through software programming, with diagnostic-level reporting that permits fault isolation down to the pin level.

However, take into account during design that it requires a JTAG connector be added to the board, and that this connector be chained together with the JTAG-compliant devices. It is the only practical option for testing BGAs because it does not require a test point on every net. It is relatively easy to generate the test programs, and thus relatively inexpensive, and comes with a one-time cost. It is fixtureless. It has powerful programming and diagnostic/debugging options both for engineering and manufacturing test departments. It gives the best of both worlds in terms of functional and ICT features.

Since BGA solder connections only can be examined through x-ray, this ability to test the BGA at the manufacturing level becomes critical. X-ray is inspection, not absolute validation. With these tools, the EMS firm can provide real-time feedback to the manufacturing floor to verify oven reflow profiles, all the more critical when processing BGAs. However, it is not capable of testing analog and passive devices.

The best test solution depends on the application and amount of money you are willing to spend. For high-reliability applications, the best solution may be a combination of these options.

Andrew Murrietta is CFO of Murrietta Circuits (murrietta.com); This email address is being protected from spambots. You need JavaScript enabled to view it.. His column appears bimonthly.

To ignore the enclosure is to miss the big picture.

Developing a competitive electronics product requires more than an innovative design of the PCB. Yes, the PCB design is extremely important and is where an OEM can add the most value to the product by squeezing more high-performance functionality in a small form factor at reduced costs. But to get that product to market efficiently requires a cooperative effort of many disciplines: PCB design, FPGA or ASIC design, mechanical design, procurement, manufacturing, software, test, etc.

Of these disciplines, perhaps the most familiar are the design of the electronics (ECAD) and the design of the enclosure (MCAD). Over the past 40 or so years, these domains have been supported by design systems that have grown like two distinct and discrete skyscrapers, each optimizing the unique design requirements of their users. This chasm between the design systems has forced extreme effort to enable ECAD and MCAD to collaborate electronically.

Collaboration started with paper being passed back and forth, and this practice still exists in many companies. Meanwhile, industry standards have been developed, such as IDF, which enables en-masse data transfer. This standard has been used to efficiently communicate objects such as the PCB outline and mounting hole locations to the ECAD designer and component placement to the MCAD designer.

In 2008, ProSTEP published a new standard that enables the bidirectional communication of proposed incremental design changes between the domains. A change could be proposed, communicated electronically to the other discipline where it could be accepted, rejected or counter-proposed. This collaborative negotiation process could continue real time until agreement was reached and the change reflected in the respective design databases.

Feeling the heat. Many factors such as excessive heat can affect the reliability of the final product. Most of these are issues that would pass through a prototype cycle and not be discovered, but the product might fail after some period of time in the field. This type of failure could have huge effects on profits, with massive warrantee or safety problems and recalls.

Heat management affecting product reliability is more of an issue than ever because of the increasing power dissipations of today’s high-performance ICs. And excessive heat over time can drastically affect product reliability in the field. Software exists that can analyze the thermal effects on the PCB and enable the designer to modify the component placement and reduce junction temperatures. But this software only can guess at the environment (enclosure) characteristics into which the PCB(s) will be placed. The design of the complete product (enclosure, fans, heat sinks, other cooling devices, etc.) exists in the MCAD domain. An analysis of the complete product is required to determine the true heat management requirements. This is not an analysis that should wait until the design of the PCB(s) or enclosure is complete. Rather, it should start at the beginning of the PCB and enclosure design and proceed concurrently throughout the product design process.

Analysis should be performed not only at the board level, but again as the PCB is mounted in the enclosure. This full product conduction and convection analysis, including the enclosure, fans, heat sink, etc., can highlight potential product hot spots and enable changes to either the parts placement or the enclosure cooling mechanisms to increase reliability. This collaboration is required to efficiently bring a reliable product to market.

ECAD and MCAD are no longer separate islands where product design can be performed in a vacuum and then data passed over the wall. For the highest performing, most profitable and reliable product design, bidirectional collaboration needs to exist throughout the design process.

John Isaac is director of market development - Systems Design Division, Mentor Graphics (mentor.com);This email address is being protected from spambots. You need JavaScript enabled to view it..