Anti-Counterfeit, Miniaturized, and Advanced Electronic Substrates for Medical Device Applications

Transcription

1 Anti-Counterfeit, Miniaturized, and Advanced Electronic Substrates for Medical Device Applications Rabindra N. Das, Frank D. Egitto, and How Lin Endicott Interconnect Technologies, Inc., 1093 Clark Street, Endicott, New York, Telephone No: , Abstract This paper discusses the development of advanced packaging that can meet the growing demand for miniaturization, high-speed performance, and flexibility for miniaturized electronic devices. In particular, recent developments in high density interconnect (HDI) substrate technology are highlighted. System-in-Package (SiP), embedded passives, stacked packages, and flex substrates are utilized to achieve significant reduction in size, weight, and power consumption (SWaP) in electronic devices. This paper also describes a Package Interposer Package (PIP) solution for integrating multiple SiPs into a single device. This mitigates the problems associated with component placement within the limited space available for individual SIP substrates. Fabrication of advanced medical substrates with technologies for parts authentication (anti-counterfeit measures) such as embedded signature circuits with zero cost adders and use of nano or micro materials as signatures are discussed. 1. Introduction: There is a strong desire to develop anti-counterfeit, advanced packaging that can meet the growing demand for miniaturization, high-speed performance, and flexibility for handheld, portable, in vivo, and implantable devices. The World Health Organization (WHO) has identified counterfeiting to be a major risk to the medical device industry [1]. Reports such as those published by the International Medical Products Anti-Counterfeiting Taskforce (IMPACT) identify and discuss in detail some of the issues involved. Tampering of electronic components is a twofold risk. First, sensitive health information stored on a device can be accessed and vital information for device operation can be altered. Secondly, replacement of components with counterfeit components can cause a device to malfunction or carry out malicious acts. The paper discusses development of proven anti-counterfeit and product authentication solutions that can be incorporated into a variety of implantable or single use and disposable medical devices. The wide range of applications for medical electronics drives unique requirements that can differ significantly from commercial & military electronics. To accomplish this, new packaging structures need to be able to integrate more dies with greater function, higher I/O counts, smaller die pad pitches, and high reliability, while being pushed into smaller and smaller footprints [2]. As a result, the microelectronics industry is moving toward alternative, innovative approaches as solutions for squeezing more function into smaller packages. In the present report, key enablers for achieving reduction in size, weight, and power (SWaP) in electronic packaging for a variety of medical applications are discussed. These enablers include materials selection, embedded passives, System-in-Package (SiP), flex and rigid-flex circuits. Manufacturing methods and materials for producing advanced organic substrates and flex along with ultra fine pitch assemblies are discussed. The paper also describes novel anti-counterfeiting approaches for the fabrication of medical devices. A variety of nano-micro composite based signature materials well suited for electronic packaging applications have been developed. These materials enable verification of authenticity with excellent control of signature properties. 2.1 Microflex and Ultra Fine Pitch Flip Chip Assembly Flexible technologies are important at all levels of microelectronics due to their desired properties, bend radius, and ability to fit within the system housing. The classification of flex is varying with its rapidly growing technological significance in electronics. Continuous technological growth and application of new complex structures are forcing changes in the limits placed on the term of classical flex. Now flex defines the technology relating to any bendable or stretchable structures or devices. The performance of flex is primarily determined by its bend radius. The final structure bend radius solely depends on dielectric layer (composition, thickness), circuit design, and number of layers. Most of the miniaturized SWaP (size, weight and power) reduction applications use high density flex circuits due to their flexibility, reduced weight, and space savings. For example, flexible solar cells, displays, and sensors typically use high density flex substrates. Multi-layer rigid structures can be converted into single or double layer high density flex structures and open up new directions for SWaP reduction in next generation technology applications. Our current flex technology is capable of fabricating a variety of flex devices by utilizing thin or ultrathin polyimide flex material and the fine line circuitization required for SWaP reduction. Circuitized solder dams help to prevent solder bridging during flip chip assembly, and is key for use of bare die in fine pitch applications. Fine line circuitization was achieved using a semi-additive, or pattern plating, process. Figure 1 illustrates SEM micrographs and a photograph of a cross section of a double-sided high density flexible substrate. Line width and spacing between lines of 11 µm are defined using a semi-additive plating process to produce metal layers having thickness of 2 to 10 µm. Vias having diameters of 25 to 50 µm are drilled through the polyimide film using a frequency-tripled Nd-YAG laser, and subsequently plated using the semi-additive plating process. The circuitized flex substrate was coated with flexible soldermask, 6-10 µm thick, on both sides of the substrate,

2 prior to placement of die and/or other surface mounted components on the flex. second building block is a joining layer. By alternating flex and joining layer in the stackup one can fabricate multilayer structure. A six metal layer structure with six single-sided flex substrates, each having thickness of 12.5 µm and five joining layers each having thikness of 25 µm, is shown in Figure 2. Total thickness of laminated multilayer flex is about 190 µm. A similar approach with double-sided flex substrates would yield a package having 12 metal layers without an appreciable increase in total laminate thickness. The current process can be used to fabricate a wide range of multilayer substrates with joining layer having PTH diameters in the range of 50 to 150 µm. Figure 2. Optical photo of a multi-layer flex substrate and corresponding cross sections. Figure 1. Top and center: SEM microghaph of circuit traces and plated vias on a flexible polyimide substrate. Bottom: Optical photo in cross section of a double-sided flex substrate with 25 µm plated vias and 11 µm wjde plated metal traces. A variety of double-layer flex substrates can be laminated together with a joining layer and subsequently drilled and plated to achieve electrical interconnection between adjacent flex substrates. Each flex can have signal, voltage, and ground planes. It is also possible to use signal, voltage, and ground features on the same plane. As a case study, 6 double layer flexes were used together with joining layers to fabricate multilayer flex substrates. Two basic building blocks are used for this case study. One is a double layer flex and the 2.2 System-in-Package Some system-in-package (SiP) designs eliminate packaged die by directly attaching the bare die to the SiP with finer pitch flip chip technology [3]. Additionally, the area used for surface mount passive components can be greatly reduced by embedding many of the capacitors and resistors into the substrate. Thinner, high-density interconnect substrate technologies with lower inductance, minimize the need for decoupling capacitors in the design. In some cases, the Printed Wiring Board (PWB) connector systems that consume large amounts of space in the board assembly can be reduced with a small pitch connector system. The overall approach is able to covert a large PWB assembly into a much smaller SiP with the full surface area on both sides of the substrate effectively utilized to mount active and passive components. For example, a high-density interconnect and embedded passivebased substrate technology combined with smaller bare die and component body sizes have been shown to result in approximately 27 times physical size reduction for existing printed wiring board assemblies, with considerable reductions in weight and power consumption (Figure 3). Reduced interconnect lengths and corresponding load is responsible for power consumption reduction. Shorter interconnect length further reduces or eliminates the need for termination resistors for some net topologies. The SiP designs can be implemented on various package levels depending on the application requirements including full systems, functional modules, MEMS sensor related packaging, and component obsolescence issues.

3 High Density Substrate Bare Die Embedded Passives Embedded Actives Size Reduction up to 27x Figure 3. SWAP reduction via System-in-Package. Figure 4. High density miniaturized circuitry enables miniaturization for increased functionality and/or decreased form factor for implantable devices High Density Substrate Technology A key technology to achieve SWaP reduction for electronics is the substrate capability to sweep components off the surface and embed them into the stack-ups. Advanced high density interconnect (HDI) features, including thin core or coreless stack-ups, small drill hole diameter, and fine feature circuitry, are required to support these flip chip components and maximize the SWaP reduction for a given assembly. Optimized wireability is achieved when dense circuitization capability (e.g., < 25 um L/S) is paired with laser drilled vias having diameters in the range of 50 um. The smaller via diameter minimizes capture pad area requirements and results in a much greater via density for substrate size reduction as compared to conventional technology. The absence of glass cloth in the dielectric generates a smoother dielectric surface finish suitable for high resolution photolithography for higher wiring density. Omission of glass cloth substantially reduces the dielectric layer thickness less for achieving much thinner stack-ups. Figure 4 shows a wirebondable miniaturized organic substrate for implantable cardiac devices such as implantable cardioverter defibrillators (ICDs) and pacemakers. A Z-axis interconnect approach is another way to achieve HDI substrates. Specifically, metal-to-metal z-axis electrical interconnection [2] among the cores of varying size or among flexible and rigid elements (rigid-flex), to form a single HDI structure is described. The structure employs an electrically conductive medium to interconnect thin cores. The cores are built in parallel, aligned, and laminated to form a variety of multilayer high density structures including rigid, rigid-rigid, rigid-flex, stacked packages, or RF substrates. Thin film resistor material can provide individual miniaturized resistors with areas as small as 0.2 mm 2. Laser trimming can produce tight tolerance resistors that possess nearly equivalent tolerance to those available in SMT packages. High Dk nanomaterials and active devices are incorporated into the stack-up to provide embedded capacitance and embedded actives, respectively. HDI substrate technology, component footprint reduction, and ability to assemble miniaturized components on dense substrates are important for significant SWaP reduction Package-Interposer-Package (PIP) Package-Interposer-Package (PIP) [4] is a 3D integration approach used for combining multiple substrates, stacked die, stacked packaged die, etc., into a single package. PIP also favors high density, complex, system integration by choosing appropriate substrate design and interconnects management. Reworkable solder-based interconnects were used for electrical interconnection between the packages. Traditional Package on Package (PoP) approaches use direct solder connections between the substrates and preclude (or limit) the use of stacked die on the bottom substrate, in order to reduce the distance between the packages to achieve finer pitch. Increasing the number of dies attached to the bottom package will increase the distance between the packages and hence will require larger solder balls to connect the packages. Larger solder ball will increase the overall package pitch. For PIP, the stability imparted by the interposer eliminates stiffener requirements, results in less warpage, reduces interconnect distance, and allows assemblers of the PIP to select the top and bottom components (substrates, die and stacked TSV die, modules) from various suppliers. This mitigates the problem associated with the warpage variation trends from room temperature to reflow temperature for different materials/processes/ substrates/modules when combined with other packages. PIP is suitable for more spaceefficient designs, and can accommodate any stacked die height on the bottom package without compromising warpage and stability. PIP can accommodate organic, ceramic, or silicon modules with single or stacked assembled die, where each module or die can be detached and replaced without affecting the rest of the construction. PIP can also accommodate heterogeneous technologies including 2D and 2.5 D technology. PIP will be appropriate for expensive high-end electronics, since a damaged, non-factional part of the package can be selectively removed and replaced. A Package- Interposer-Package (PIP) test vehicle was fabricated by alternating four packages and three interposers in the lay-up and joining them together with solder using a reflow process. PIP requires at least (n-1) number of interposers for n number of packages. Figure 5 shows extended PIP structures for

4 connecting four (n) packages with three (n-1) interposers using solder-based interconnection. An optical photo of the extended PIP structure is shown in Figure 6. Figure 8 shows a PIP concept of breaking a complex expensive high-end electronic structure into SiP-interposer- SiP prior to attach to a low end board construction. Figure 5: Schematic cross section of package-interposer- Package (PIP) construction with 4 packages and 3 interposers. Figure 6: Photograph of Package-Interposer-Package (PIP) construction with mujltiple packages and interposers. Figure 7: 3D integration of system-in-package (SiP) (before and after assembly) D Integration of System-in-Package (SiP) The miniaturized SiP with its reduced substrate size having embedded passives provides a high wireability package with excellent communication from top to bottom and facilitates double side assembly approach. When converting larger PCBs to miniaturized SiP assemblies, there may be issues with insufficient space to accommodate all the components. In the present paper, a multiple SiP approach is applied to accommodate all the components, and interposers are used in a 3D-integration of these multiple SiP to provide a SiP- Interposer-SiP construction, an unique solution for next generation complex packaging. Figure 7 and Figure 8 represent two high-density double-sided assembled circular SiP substrates attached with each other using an interposer to produce a 3D SiP-Interposer-SiP construction. PIP construction using various miniaturized assembled packages (SiP) can be attached to a board to generate 3D architecture. The 3D integration method can be used to attach, repair, or upgrade individual assembled packages (SiP) in the stack.

5 Figure 8: SiP-Interposer-SiP construction (before and after assembly) prior to attach to a low end board. 2.6 Anti-Counterfeit Advanced Packaging This paper also reports novel anti-counterfeiting approaches for the fabrication of advanced packaging. There are several anti-counterfeit signature approaches possible, but applying them to the manufacturing environment is critical. The manufacturing environment requires faster and cheaper ways to detect the components. Furthermore, processing cost of anti-counterfeit signatures sometimes limits their application. Fabrication of advanced packaging with parts authentication technologies such as embedded signature circuits with zero cost adders and signature nano or micro materials possess these desired attributes of anti-counterfeit measures. Nano-micro material based signature marks can provide protection for components in a manufacturing environment. Individualized custom nano-micro materials can be developed and applied as printable ink, printable paste, or coatings to a host of carriers. Nano-micro materials with specific optical and or electrical properties can be used to provide a secure signature for many security applications. They can help protect the quality and integrity of products by virtually protecting any item throughout the supply chain. We have identified a nano-micro material system that provides optical/electrical response characteristics. Optical response depends on the ingredients of the nano-micro materials. Figure 9 illustrates white ID on a component s surface and its optical response characteristics. This concept is useful for producing multiple colors from the same white ID, and each color can be used to represent an individual number for making it more secure approach. Figure 10 shows another option of anti-counterfeiting using multifunctional nano-micro materials. Here we have used electrical and optical response characteristics as anti counterfeit measures. Figure 9: Top: white ID, Bottom: optical signature. Figure 10: Multifunctional nano-micro materials. Electrical and optical signature response (Inset : White ID prior to optical response). There is a significant additional manufacturing cost adder for deploying most anti-counterfeit measures in electronic components. However, by embedding unique electronic signatures in circuit traces, one can easily authenticate parts with the presence of expected signatures. The signature creation process is simply accomplished at the component artwork generation stage. Small circuit signatures are purposely introduced in one or more selected traces at the creation of artworks. There is no cost adder for manufacturing these components since they are formed concurrently with the functional circuits. The small circuit signatures do not adversely affect normal circuit function, and they resemble other common, naturally occurring defects found in substrates and PCBs. The camouflage characteristic of this anticounterfeit technology offers an added level of protection. A signature analyzer designed specifically for this application is used to excite the selected circuit traces and acquire the resulting signatures. The two ends of the circuit trace under

6 test are probed with this analyzer. A low frequency AC signals is injected into the circuit trace and the low level modulated harmonics are acquired and analyzed. The composite amplitude and phase angle modulation of the harmonics (signatures) are largely dependent on the construction and makeup of the substrate/pwb. The observable normal harmonic modulation of the excitation signals (Reference Baseline) are uniquely produced due to the specific substrate material sets used, conductor resistivity, cross-section geometry and the length of the traces. The presence of an anti-counterfeit signature in the selected circuit traces cause additional harmonic modulation above the Reference Baseline signal level. Therefore authentic parts can be identified easily using the signature analyzer by comparing detected circuit trace signatures to that stored in the database for this specific component. Typical data collected utilizing this technology is shown in Figure 11. wiring density with the fine line circuitry required for ultra fine pitch flip chip assembly. A PIP approach was developed for 3D integration of various system-in-package (SiP) constructions. This approach is favorable for miniaturized expensive electronics where part of the package or system, if necessary, can be replaced or repaired, or even upgraded without compromising overall electrical performance. A variety of signature responses well suited for electronic packaging applications have been developed that enable verification of authenticity with excellent control of signature properties. Acknowledgments The authors acknowledge the valuable contributions of J. Hoang, E. Kopp. B. Bonitz, F. Marconi,B. Wilson, B. Pennington, and M. Shay. References F.D. Egitto, S.R. Krasniak, K.J. Blackwell, and S.G. Rosser, Z-Axis Interconnection for Enhanced Wiring in Organic Laminate Electronic Packages, Proceedings Fifty-Fifth Electronic Components and Technology Conference, May 31 to June 3, 2005, Lake Buena Vista, FL (IEEE, Piscataway, NJ, USA), p Steven G. Rosser, Irving Memis and Harry Von Hofen, Migrating Printed Wiring Board Assemblies into System in a Package (SiP) IMAPS 41 st International Symposium on Microelectronics, November Rabindra N. Das, Frank D. Egitto, Barry Bonitz, Mark D. Poliks, and Voya R. Markovich, Package-Interposer- Package (PIP): A Breakthrough Package-on-Package (PoP) Technology for High End Electronics 61 st Electronic Components and Technology Conference proceedings, (June 1-4, 2011). Figure 11: Measurement results of identically constructed traces with and without embedded anti-counterfeit signatures 3. Conclusions: Miniaturization of electronic devices are driving the packaging need for achieving increased functionality with decreasing size, weight and power (SWaP). Advanced substrate technology with novel interconnection cross sections, embedded passives and actives, and 3D integration solutions have been successfully implemented to reduce electronics volume and advance the capabilities of electronic device technology. For advanced flex and rigid-flex circuit constructions, high resolution photolithography and semiadditive plating processes, are important to achieve higher