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3T Institutenweg 6 NL-7521 PK Enschede T +31 (0)53-433 66 33 F +31 (0)53-433 68 69 [email protected]

IMA Kilian

High resolution data logger inside tablet punch The force at which powder is compressed to a tablet influences the effect of the medicine: Does the tablet solve in the mouth, in the stomach or not at all? KILIAN & Co. GmbH, manufacturer of tablet presses, which produce up to 1 million tablets per hour, consulted the IVAM NRW network to develop a measurement and data application small enough to fit inside one of their tablet punches. 3T has accepted this challenge and now develops a data logger that fits a 6 cubic cm cylinder inside a punch to measure and log 2 million force samples in 80 seconds. The challenge requires the cooperation of micro techniques in an unconventional way. In 1999 KILIAN contacted 3T to help them with measuring important process parameters, like tablet compression force and acceleration of the punches during operation. A so called Instrumented Punch must be able to measure and record these properties without contact to the outside world and without interfering in the normal operation of the tablet press. 3T's mission statement; development of products and systems on customer specification for measurement, control and data-applications using microelectronics, sensor technology and microtechnology, clearly indicates the expertise that was necessary to help KILIAN with their measurement problem: · systems on customer specification · measurement with direct data storage · use of micro techniques. In the Twente area a mix of companies with a history of co-development, consisting of 3T, MASER and ELECT was found to develop and produce around fifty instrumented punches a year. Instrumented Punch New about this punch is that process critical parameters can be derived directly from within a normal production process. Since punches are universal for every machine type, the Instrumented Punch can be easily installed without changes to the machine. All a machine operator has to do, is replace one of the punches in a machine with the Instrumented version. All electronics and sensors are built inside the punch, so it can be used as a normal punch to produce tablets. Data can be extracted from the punch by removing it from the machine and placing it in a cradle unit that connects to a PC. An advantage of in-process measurements is the ability to measure all forces that are necessary during the production of a tablet. In the past it was only possible to apply each position with an individual sensor, now it is possible to measure all the different forces with only one sensor. This is the precompression force, the maincompression force and the force that is applied to eject the tablet. In other words how much does the tablet stick to the punch. The new instrumented punch will be used to find the correct recipes for tablet development. Simply install the punch, run a batch of tablets, take out the punch and read out the data. While reading the data, the internal battery will be recharged. Most important is the improvement of the usability. In the past the machine had to be adapted to measure the forces, now every operator can

do that job in an arbitrary machine. To obtain this functionality, all data is stored in the punch itself and read out after use, making it a miniature data logger. The sensor is a strain gauge bridge at the neck of the punch tip. This major step, downsizing all electronics to fit inside the punch, can only be made because of the advancing miniaturization of electronics and a good overview of the availability of small but multifunctional components nowadays.

Challenges In the development there are several problems to be solved. All have to do with the available amount of space, a cylinder of 11 mm diameter and 60 mm length. In this cylinder, which is the maximum space that can be hollowed out in a punch without affecting its strength, the entire data logging electronics needs to be realized. The requirements for the signal-processing unit are also challenging: 16bit accuracy at a sample rate of 25 kS/s. The most important components are: · 8-bit RISC Microprocessor to control all measurements · 32 MBit flash memory to store the data · Single cell power supply · Signal conditioning electronics · AD conversion Just the battery alone occupies at least 1/3 of the available space, leaving even less for the electronics. The biggest problem appeared to be the 11 mm diameter: The required microprocessor and the memory are housed in packages larger than 11 mm, so the electronics will never fit. It is a problem that becomes more common nowadays; the sensors are made small, but what about the electronics? Sometimes an ASIC can bring relief, but the development of an ASIC is not always possible.

The solution can be found in the use of the components as naked die, that is without the package, if available. In this case the naked die will fit into the cylinder easily, so with some clever connecting and routing, the use of flexfoil, serial communication and using the minimum amount of components it should fit. But what if the components are not available as naked die? Can you take the die out of the package and re-use it? Out of the package: just do it Most manufacturers are willing to deliver naked dies, but only in quantities starting at 10.000 pieces. For a estimated production of 50 punches per year, this is not acceptable. Together with MASER in Enschede, the Netherlands, specialist in micro-electronics analysis, the microprocessor and the memory chip will be taken out of their package. Normally this decapping is considered destructive, and these naked dies are normally not re-used. But for KILIAN's punch there is no other choice. So an analysis of the problems concerning the re-use of de-capped die has been made: The biggest problem in re-using the die lies in the connections. The bonds that were used to connect the die to the leads leave traces of gold on the bondpads, making it necessary to bond the die again with gold. However the naked die has to be bonded to the circuit board at low temperatures to save the PCB. Normally this requires the use of aluminium instead of gold. ELECT in Weerselo, the Netherlands, specialist in chip-onboard, has developed a recipe for gold bonding of naked dies at lower temperatures. Micro techniques will be used in an unconventional way in the no-man'sland in between established technologies. Worlds smallest? The instrumented punch is still in a development phase, a lot of steps have to be taken before the first punch will be realized. The small size brings forward not only the package problem described above, but also inductive cross-talk between components and related problems of more practical nature. At the ACHEMA 2000 in Frankfurt the first prototype has been functional, the rest of the year 2000 has been used to complete the prototype phase. Within a few months this self powered 16 bit data logger with 32 MBit of memory will be a fact.


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