To read the first part of this article, click here.
Having already moderated Session 2, the moderator turned presenter as Emma Hudson, UL’s industry leader for PCBs in Europe, the Middle East, Africa and Latin America, continued her campaign to help the industry to understand the significance of solder limits and the need to keep them updated to meaningfully reflect the conditions of the assembly process.
She explained that Solder Limits were critical parameters employed in most of the test procedures used to characterise a PCB, a metal-clad base material or a solder resist, as part of the Recognition process, and represented the soldering processes the PCB would be exposed to during component-assembly operations. Any component-assembly time spent over 100°C or the maximum operating temperature, whichever was greater, was considered to be part of the Solder Limits, which could be single time and temperature or multiple times and temperatures. The only exceptions were PCBs which would only be subject to hand soldering.
The PCB industry was well aware that the more severe the soldering operation, the greater the degradation of the PCB and this included the properties evaluated for UL Recognition. Hudson emphasised that the traditional solder float test was not representative of SMT soldering operations. She made it clear that the standards were not changing, and that Solder Limits had always represented the soldering processes the circuit board was exposed to during the assembly operations. And manufacturers of PCBs, laminates and solder resists were free to choose their solder limits provided they were meaningful. Importantly, exceeding the Solder Limits would breach the Conditions of Acceptability and the PCB would be no longer Recognised for that application.
The fact was that the majority of UL Recognized PCBs, laminates and coatings had not had their solder limits updated for surface mount and/or multiple soldering operations and testing under more severe conditions would be required, the amount of testing depending on the materials being used and the existing parameters and process conditions. If laminate and coating manufacturers established appropriate solder limits, this would reduce the amount of testing to be carried out by the PCB fabricator.
Hudson urged the industry to work together to determine what would be the most meaningful solder limits to have Recognized. UL planned to formally communicate to companies that currently had UL Recognition or UL Listing. UL field engineers would then be responsible for verifying the soldering conditions to which the PCBs were exposed during all assembly operations and comparing these to the solder limits Recognized for the PCB. If the Recognized solder limits were exceeded, a Variation Notice would be raised. There would be a two-year transition period for the industry to complete the updating of their solder limits, after which a Variation Notice would result in charges being incurred.
Session 4 focused on new PCB material and processes for advanced applications, and was moderated by Martyn Gaudion, managing director of Polar Instruments and EIPC board member.
“Why going to halogen-free laminates?” Was the question posed by Shannon Juan, product promotion and marketing manager for Elite Material Co. in Taiwan. She explained that the development of halogen-free laminates had been driven initially by increasing environmental awareness and international environmental protection regulations. The adoption of halogen-free by leading manufacturers of mobile phones and computers may have been motivated primarily by commercial rather than technical considerations but had served to give halogen-free a firm foot-hold in the laminate market.
So how did halogen-free laminate differ from its halogenated counterparts? How was flame retardancy achieved without brominated resin? Juan examined the chemistry of combustion and explained that the essential components were combustible matter, a heat source and a combustion-supporting gas. Combustion in oxygen was a chain reaction involving many distinct radical intermediates. The combustion reaction could be disrupted by inhibiting the chain reaction, or by producing an incombustible gas or water to reduce the temperature, or by producing a char to separate the combustion-supporting gas from the combustible matter. Halogenated material acted by blocking the chain reaction, whereas halogen-free tended to rely on the production of a thick char and/or a filler that produced water vapour.
She showed some test results demonstrating superior physical properties of halogen-free resulting from stronger molecular bonds, and claimed that in general, halogen-free materials had better thermal reliability than their halogenated counterparts. And in conclusion she suggested that, in addition to its better reliability, as environmental awareness attracted more attention, halogen free material would become a trend for the future.
Alexander Ippich, technical director signal integrity and advanced technology in the OEM marketing group at Isola, discussed how laminate and process technology could be optimised to minimize the RF impact of frequencies in the 55 GHz to 95 GHz region.
In RF and microwave applications, most critical signals were routed as surface microstrip transmission lines without solder mask coverage to minimize insertion losses. However, the absence of solder mask resulted in these critical traces being coated with the solderable final finish, typically ENIG.
In the interests of keeping insertion losses to a minimum, very-low-loss and ultra-low-loss laminates, with dissipation factors as low as 0.0017 and very smooth copper foils were used in these high-frequency applications. But the impact of final metallisation was often not taken into consideration, and in the case of ENIG, the lower conductivity of the nickel could cause excessive losses as a consequence of the skin effect concentrating the current in the conductor surface.
The effect of surface finishes on insertion losses in the of 55 GHz to 95 GHz frequency range was studied in a Design of Experiment with six different chemistries, on a test board fabricated on one of Isola’s ultra-low-loss, woven glass reinforced, thermoset laminates. The following finishes were evaluated: electroless nickel immersion gold (ENIG), organic solderability protective (OSP), immersion tin (i-Sn), immersion silver (i-Ag), palladium gold (Pd-Au) and immersion silver immersion gold (ISIG). The coupons were tested with a vector network analyser, sweeping from 55 GHz to 95 GHz and collecting 2-port S-parameter data sets.
The results clearly indicated ENIG to give the worst insertion losses by a substantial margin. Of the non-nickel finishes, immersion silver gave the best results, but only marginally better than OSP and ISIG, and significantly better than immersion tin.
Ippich concluded by commenting that although designers were very aware of the effects of laminate properties and foil roughness, the choice of solderable finish was an important consideration when optimising a design to minimise insertion losses.
The first day’s conference programme concluded with something refreshingly different: a presentation that might be categorised as more philosophical than technical. Russell Morgan, Service Designer at Verisure in Sweden, captured the attention of delegates and subtly encouraged them to think laterally rather than logically as he considered the role of design in the IoT exemplar of the connected home. “User experiences happen whether you have designed them or not.”
He commented that there had been an explosion of entrants into the Smart Home market, providing Internet of Things (IoT) devices that generally fell into two categories: “enablers” that provided information to allow something else to happen, and “transformers” that turned traditional devices into Smart devices. From a designer’s point of view, IoT was not so much a hardware problem, but more a human interface problem. Taking smoke alarms as an example, whereas children would probably sleep through a traditional alarm, they would be woken by the sound of a human female voice. Different people needed different services and devices, and customer experience mattered more than ever—delight stemmed from meaning, not function!
Morgan considered that service consisted of three parts: before, during and after the event—the expectations, the experiences and the consequences. The experiences were a composite of what happened with the expected outcomes and the unexpected outcomes, whether positive or negative. “How can we overcome trust when people don’t trust the technology?”
In his view, successful design relied on finding a balance between validation and optimisation: “How do we know when our initiatives are worthwhile? Are we solving a real problem?” and “How do we know they are being executed in a usable way? Does the feature set of the product map back to a compelling need in the mind of customers and users?”
In his IoT exemplar of the connected home, Morgan believed that the progression of economic value needed to be revisited. The work of design and staging many competing experiences into one seamless experience meant that the initial focus needed to shift from goods and services into defining experiences and understanding the context in which they would be lived through.
“It is only when we put the customer experience first that goods and services truly fit seamlessly into peoples’ homes. Great design is the driving force behind this!”
A long conference day was followed by a long evening, as delegates moved quickly from conference room to bus, for a 60km trip through the late afternoon traffic to Unimicron’s superb new innerlayer factory in Geldern. Welcomed by Unimicron CTO Rico Schlüter, the party was split into small groups and given guided tours of the facility.
And afterwards, back on the bus to a reception and conference dinner at the historic Castle Walbeck, where the highlight was a tribute to the long and dedicated service of Michael Weinhold, taking his well-earned retirement from the position of EIPC technical director.
It took some persuading to get everyone back on the bus to Dusseldorf, but no-one was left behind, and we were home by midnight. A brilliant day’s experience all round!
Photography by Alun Morgan