According to Tom Zednicek and Radim Uher of AVX Czech Republic facility in Lanskroun- embedded ceramic capacitor technology has finally begun the important transition to mass production in printed circuit boards where volumetric efficiency is of keen importance. In their technical paper – “Ultrathin Discrete Capacitors for Emerging Embedded Technology,” Mr. Zednicek and Mr. Uher cite the growing needs of the wireless handset industry to free up much needed board space to enhance product functionality by placing ceramic capacitors between the interconnecting substrates of the printed circuit board- a three-dimensional approach to board development and design. Stating that passive components account for as much as 70% of the board space on any given electronic product; but that both sides of the printed circuit board are reaching their physical limitations of space. To solve this problem, AVX has noted that anywhere from 50 to 150 of the ceramic capacitors commonly used in wireless handsets could in fact be embedded with technology that already exists today. Furthermore, AVX notes that embedding is the next logical step in effective miniaturization, given the fact that over the past 20 years the available case sizes of MLCC have declined in physical size from 0805 to 0201 and even 01005 (EIA measurements). AVX notes that one of the primary limitations in employing embedded capacitance is cost, however, they note that when a total systems view is taken of cost to produce a printed circuit board, that embedded capacitance may in fact be more cost effective when pick and place costs of handling ultra-small components is considered; and in addition, cost savings may be enhanced when yield ratios and rework is also considered when comparing costs associated with traditional methods of creating today’s printed circuit boards.
AVX notes that one of the most difficult technical aspects of creating embedded capacitance is the thickness of the component. The company notes that the movement among handset manufacturers is to have capacitors no thicker than 150 µm accepted as the standard component height for embedding. To accomplish this, consideration must be given to the termination of the component, which traditionally creates a variation on the overall thickness of the part. To overcome this variation, AVX has developed a new Fine Copper Technology technique which allows for the creation of a very thin and flat termination layer. Copper layer terminations have also been proven to be the most suitable and appropriate for the embedding technology process.
With respect to the technology availability and the capacitors most commonly used in the wireless handset industry today, there are two capacitance values that are of greatest interest to printed circuit board suppliers today- these are the 10 nanofarad and the 100 nanofarad MLCC devices with a rated voltage of 6.3 Vdc with X5R performance characteristics. To embed these capacitors during the PCB assembly process, individual components are placed onto pre-prepared copper foil in a specific pattern according to the intended design; then step-by-step treated foils of substrate are placed around and on-top of components followed by another step of copper foil. By applying pressure and elevated temperature the “sandwich” is laminated together to create the core of the printed circuit board. The final step is to create copper tracks and layers into the required circuits and then the final construction of the printed circuit board is achieved using traditional PCB manufacturing techniques.
AVX notes that some of the advantages of applying embedded capacitance in a PCB include the following:
• Improvement of electrical parameters because of shorter distances between components.
• Increased component reliability because the components are encapsulated in a protective environment.
• Better resistance to mechanical stress.
• Improved thermal properties due to better heat sinking.
AVX also notes some of the challenges associated with embedded capacitance include the requirement of 3D design skills by the PCB manufacturer and the number of vendors offering capacitors suitable for embedding remains limited.
In the future AVX envisions the requirement for embedding larger capacitance chips in smaller case sizes, with the 1 microfarad, 6.3 volt capacitor in the 0402 case size as a logical direction of the technology. This may provide the impetus for other capacitor dielectrics- mainly tantalum, to enter the field of embedded capacitance in the future
Additional Resources: (1)
Integrated Passive Devices: World Markets: 2003-2008 ISBN # 1-893211-61-4 (2003)