The specialist for printed circuit boards Würth Elektronik integrates cantilevers operating as a sensor, integrated in the PCB, allowing new industrial applications. This technological innovation has been made possible due to an in-house conductive polymer, i.e. thick film polymer paste, enabling the necessary application intelligence structured in to a specific designed printed circuit board.
This trendsetting, advanced solution is characterised by a high potential of technical innovations. It is suited to numerous new and customized applications, e.g. allocation and identification tools in ERP systems. The first serial products are already approved. Demo boards will be on display for the first time at Würth Elektronik’s stand No. 424 in hall 9 at the SMT in Nuremberg, taking place on the 5thuntil the 9thof May.
Currently existing cantilevers are limited to simple functions, e.g. pure force measurement, Würth Elektronik has innovated and upgraded this no longer limited technology.
By means of resistive strain gauges printed on the PCB and integrated sensor and electronics on board, the new cantilever also replaces the weaknesses of traditional capacitive sensors for allocation systems, e.g. insufficient robustness against environmental conditions. Precisely due to this robustness, the cantilever with polymer strain gauge is suitable for applications that are subject to special demands in terms of temperature, humidity, industrial climate and similar.
Würth Elektronik, with their thick film circuits on PCBs using conductive polymer paste, is a genuine pioneer in this still young field.
These cantilevers, which can be integrated into any PCB type (i.e. double-sided, multilayer, HDI or flex-rigid), are commonly used as short stroke sensors and force indicating devices, as well as making integrated pressure sensors possible.
The special technique of embedding the polymer hybrid as a screen-printed, passive component inside internal layers of a PCB, provides a level of high packing density combined with reliable connections to conductive traces never before experienced.
Innovative polymer thick film system allows less development efforts in time and costs at no compromise in Quality and robustness
The crucial factor to this further integration level is the in-house developed and secret conductive plastic paste with up until now unknown new features. By applying new conductive and other polymer types with targeted electrical characteristics, Würth Elektronik succeeded in printing passive components on board and integrating sensors inside the PCB. This technology enables the development of customized solutions, which, among other items, reduce space and volume as well as production efforts at a considerable extent. Development time and costs are reduced while simultaneously improving the end application robustness.
Frank Dietrich, head of the product division FLATcomp systems at Würth Elektronik and developer of the specific “smart conductive“-polymer paste, points out: „The customer does not get the paste in the actual sense, but the cured thick film, therefore we use the correct term PTF (Polymer Thick Film). We are tending more and more towards this variation of thick film due to the wide range of resistance it offers; in the future we will have many passive components screen printed on the PCB.”
For polymer strain gauges, the thick coating creates an exceptionally stress-sensitive resistor; achieving output signals 50 times higher than a conventional strain gauge’s signal, and therefore needs only a low level of amplification.
With this, Würth Elektronik is able to generate a thick film strain gauge on the PCB so that the integration of sensor and evaluation electronics within the compact design of a mechanically structured PCB becomes possible.
The advantages of this integration are outperforming all former approaches for improving sensor technology: The designer enjoys great creative freedom and needs less time for development; the sensor is positioned close to the electronic evaluation unit; the PCB is capable of taking over several functions; the solution gives high reliability and the start-up costs are reduced.
Moving forward with integration really pays off here, since more than 80% of all components are passive components, occupying more than 35% of space available and more than 25% of all solder joints in assemblies. Reduction of solder joints means improvement of the products’ reliability and robustness.
Thick Film strain gauge combined with cantilever in comparison
Strain gauges usually are glued onto metal cantilevers. Designed as a Wheatstone bridge, a signal corresponding to the proportional value of the force effect on the cantilever is transferred. Commercially available strain gauges are available at values between 1 mV/V and 4 mV/V. The practical consequence is, that the signal needs to be amplified by 250 to 1000 times before it becomes fit for purpose.
Moreover, side effects like drifting and EMC interferences become more likely with a high amplification.
On the other hand, the printed polymer strain gauge with structured PCB (applied for patent) utilises the TK-compensation due to the Wheatstone bridge and the matching of FR4 to the conductive polymer. The signal obtained using this method is around 50 times higher than for conventional strain gauges. Conclusion: Only a slight amplification is needed. In many applications, even amplification becomes no longer necessary, resulting in cost savings, higher reliability and less interference. As with printed resistors, the application becomes more robust. This type of sensor may be also used as short stroke sensors or combined with a diaphragm - as a pressure sensor. Equally, it is possible to replace simple position switches using this PCB element, both cost-effectively and with reduced interference.
Peter Tiefenbach, head of the product management Polymer technology FLATcomp at Würth Elektronik, says: „The printed circuit board takes over functions, playing the role of a sensor. That generates an essential difference: The PCB is not applied as backing material for electronic components or as a connecting element; nowadays it is considered a valuable system, able to take on additional tasks. Advancing functionality this is one of the basic technological principles today. “
Practical application of the new cantilever technology
The integration of the aforementioned new functions into the printed circuit boards has passed the first practical tests. Field application tests and approvals for serial production of customer-specific solutions have already been carried out. A typical field of application is allocation systems for ERP-systems in any environment. For highly frequented store shelves with a high turnover rate it is important to know the number of goods available at a specific time. Würth Elektronik offers a convenient, cost-effective and manufacturable solution with the printed circuit boards including a sensory cantilever, with both individual and universal design possibilities, dependent on the quantity of units intended for shelf placement. Though the basic idea is not new, it fell through in the past due to a lack of reliable and affordable sensor technology.
One of Würth Elektronik’s customers has tested their system, in which at 5.6 grams the sensor transfers an “empty shelf” signal to the central controlling unit. Whereas staff employees were previously always having to run up and down the rows of shelves, to check and refill them, i.e. a number of observations had to be made simultaneously Würth Elektronik’s system solution now simply sends out a short message informing - for example - that the shelves No. 1 to 15 are only half full.
In comparison to such quantifiable information, capacitive systems of earlier generation applied applications provide only simple information like “full” or “empty” / “yes/no”. Moreover, they would not work in a humid environment, due to physical and other reasons, just another argument why some customers moved to the environment-robust solution supplied by Würth Elektronik. Visibly proud, Frank Dietrich says: “We managed to create all these intelligent applications and solutions only by reverting to our proprietary paste systems with new and unique characteristics now available just at Wuerth Electronic.”
New Zeitgeist: Problem solving through best customer-supplier relationship.
Until now, this technology has only been known by insiders, still waiting for global acceptance, mainly due to the small number of providers requiring a close partnership between customer and producer. “Obviously, this means of engagement no longer fits in with the current cultural climate”, says Peter Tiefenbach,” however, Würth Elektronik senses a significant change of mind. In many cases, reliability and service are becoming more important than just the price. Partnership and competence in finding solutions once again are becoming best selling arguments. ”
Tiefenbach also assigns this returning awareness of the future oriented changing role from a straight PCB-provider to a problem solver and close partner of customers; Würth Elektronik is proving exemplary in performing this role and is receiving great feed-back from the market: „Firstly, many customers are not aware of the technological opportunities available, sometimes they see their own problems in the wrong light, ask for their resolution by using obsolete techniques; or they ask for products that do not meet their actual demands. Thanks to our innovation-based and increasing problem solving skills and customer awareness, we are able to detect the actual problem upon careful investigation, developing a customer specific solution that customers may not have perceived as an existing option.”
Würth Elektronik enjoys a particular competitive advantage during the development of customer specific solutions, not only due to their exclusive availability of intelligent paste - which makes the big difference, but also due to their ability for the development and supply of comfortable one-stop, on site solutions, with access to an existing, well established and fully developed infrastructure and state-of-the-art equipment.
For further information on Wuerth Elektronik´s cantilever sensors please visit us at: www.we-online.com/flatcomp/
About Würth Elektronik
The Würth Elektronik Group of companies is a globally acting and independent member of the Würth Group, producing PCBs, passive and electro-mechanical components and electronic assemblies in press-fit technology. Beside their own R&D, Würth Elektronik is also involved in numerous external research communities, e.g. KRAFAS or TIPS. Additionally, their business unit Würth Solar, the world-wide first producer of CIS- photovoltaic modules in large volumes and provider of complete solar power systems, is part of the Group of Companies. Würth Elektronik employs around 6000 personnel worldwide.
Wuerth Elektronik GmbH & Co. KG
1. WE Drying Process
Here the PCB is entering the drying or burn-in process to cure the thick film. Frank Dietrich, head of FLATcomp systems at Würth Elektronik and developer of the special “smart conductive“-polymer-paste, points out: „The customer does not get the paste in the actual sense, but the cured thick film, consequently we are using the correct term of thick film or PTF (Polymer Thick Film). We are tending more and more towards this variation of thick film due to the wide range of resistance it offers.”
2. Cantilever Function
The cantilever utilises the function of a „Wheatstone Bridge”
Image 1: The resistance increases in the tension zone and decreases in the pressure zone.
Image 2: Increasing resistance in the pressure zone; decreasing resistance in the tension zone.
Since there are two potential dividers, the signal change doubles. The same resistor material at the same position with an identical TK leads to a reduced TK of the system.
The FEA (Finite Element Analysis) shows the various levels of external stress loaded on a component in different colours (here by bending). The analysis shows the position required for the polymer-DMS.
4. WE_PCB buffer
Würth Elektronik relies on sophisticated machinery: The picture shows the PCB buffer unit inside the fully automated clean room production line.
5. WE_Screen print
The “smart conductive” polymer paste is coated by screen-printing, this allows printing passive components on the board and the integration of sensors inside the PCB.
6. WE_Hands-off line
Competitive advantages: The polymer paste (kept as a secret) along with a fully developed infrastructure, state-of-the-art machinery, is realising fully-automised, customised complete solutions.
Note: The above text is the public part of the press release obtained from the manufacturer (with minor modifications). EETimes Europe cannot be held responsible for the claims and statements made by the manufacturer. The text is intended as a supplement to the new product presentations in EETimes Europe magazine.