Laminate PCBs (rigid, flexible, and rigid-flex) is the substrate of choice for 90% of medical device applications. Executed correctly, laminate substrates are compatible with chip & wire, SMT, flip-chip assembly technologies, and any combination of those. Nevertheless, not every material / layout combination works for the specific application and not every board house is capable of manufacturing PCBs to challenging specifications. Teledyne Medical designs PCB substrates in-house and sources the boards from a variety of qualified suppliers across the globe. Since the board design is an integral part of the module design, all process, quality and performance demands are incorporated and guaranteed by Teledyne Medical.

Rigid PCBs are based on glass fiber-reinforced polymer sheets. The exact polymer material (epoxy, BT, polyimide, etc.) strongly affects mechanical, thermal, and electrical properties of the PCB and has to be chosen very carefully, depending on the application. Rigid PCBs are the easiest to use in the routine electronic assembly, particularly when board dimensions are relatively large. Correctly designed stacked PCBs can provide extremely high volumetric density of the electronic assembly. On the downside, rigid PCBs have a tendency to warp, when exposed to higher process temperatures. For extremely dense designs, the presence of the glass fiber puts a lower limit on size and technology of the layer-to-layer vias.

Flexible PCBs (also known as flex) are based on non-reinforced polyimide tape (other, esoteric tape materials also exist). Flex boards can be bent, at angles and radii which are a function of the board thickness and lay-out. Consequently, flex is always considered for the designs involving stacking and folding. The other major advantage of flex is it's compatibility with laser or plasma drilled microvias, leading to extremely dense "build-up" PCBs. In a small form factor, flex boards can be almost as rigid as their "rigid" counterparts of similar thickness. At the same time, very thin or relatively large flex panels lack the intrinsic rigidity desired for assembly processes and thus require specialized tooling. Design and fabrication of the dense flexible boards require special attention and skill - fully warranted by the end-result.

Rigid-flex PCBs consist of the co-laminated rigid panels and flexible cables. They combine the rigidity and stability of the rigid boards with flexible segment-to-segment connections provided by flex. Rigid-flex boards are most beneficial when relatively large boards are connected by multiple signal lines without a need for tight, large angle bends. As such, they are widely used in back-plane assemblies. For miniaturized 3D designs, the inevitable compromises of the rigid-flex can offset perceived advantages, and properly executed rigid or flex assemblies will perform better.

Ceramic and ceramic / glass substrates are a staple of high-reliability electronics and has traditionally been used in long-term implant applications. The major advantages of ceramics versus polymer substrates are their stability under environmental conditions (including in-process), better thermo-mechanical performance, lower losses at RF frequencies, and embedded passive elements. That said, improvements in PCB technology are leading to displacement of ceramic substrates from all but the most demanding applications where a convolution of multiple requirements makes ceramic the most technological and cost-effective solution.

Ceramics are generally compatible with all existing assembly technologies. Two general types of ceramic substrates exist - thick film multilayer build-up and co-fired (high- and low-temperature). Teledyne has been perfecting build-up technology for the past 40 years and has a fine-line fabrication facility on site. We also have many years of experience designing co-fired substrates and working with the limited number of co-fired ceramic suppliers world-wide. The third, not as widely used substrate type is thin-film (photolithographic) ceramic. With new developments in thick-film technology, thin-films ceramics are most useful when embedded, ultra-high stability resistors are required.

Multi-layer ceramics are built by sequential deposition of the conductor and dielectric layers on top of the ceramic wafer (usually Al2O3). The layers are deposited in the form of a thick paste which, when sintered at high temperature, exhibit the properties of the solid material (metal or oxide-dielectric respectively). The traditional deposition technique is screen printing. This technique is conducive to creating substrates with very high layer counts (up to 24), but limits the definition of the smaller circuit features. When those are required, multiple types of photo-definable thick-film technologies can be used, which combine traditional printing and photolithography. With decades of know-how and extensive facilities in thick-film technology Teledyne is capable of producing the most challenging thick-film designs. We are also often used as a beta-site for the developers of paste materials.

High-temperature (HTCC) and low-temperature (LTCC) co-fired ceramic substrates are manufactured by co-lamination (co-firing) of the ceramic dielectric sheets ("green tape"), with metal layers printed on top of the tape prior to lamination. The main advantage of co-fired technology as compared to the multi-layer build-up is that it allows larger format processing and a single firing step, leading to a more economical cost structure at high volumes. The difference between HTCC and LTCC is in firing temperature as well as the base dielectric and conductor materials: alumina and tungsten for HTCC and ceramic/glass and gold/silver for LTCC. HTCC is a much older technology; LTCC is used primarily for its dielectric and conduction properties in RF applications. HTCC can almost be considered as PCB of the ceramic world because it counts on the metal surface finish to ensure compatibility with the assembly processes and materials. Since conductor patterns in co-fired ceramics are printed, fine-feature resolution achievable in thick-film technology is not feasible for either HTCC or LTCC. Also, since most of the reputable co-fired ceramics manufacturing is consolidated in Japan, one must account for months of lead time, and multiple tens of thousands of dollars in tooling costs.

Thin film ceramics are based on photolithography of the metal and oxide layers on top of the ceramic wafer. Highly stable ceramic resistors and resistor networks procurable through component manufacturing are based on this technology. For generic applications it offers marginal advantage over photo-definable thick-film substrates at 10x the costs.

Surface Mount Technology (SMT) is the most commonly used electronic technology and consists of soldering various active and passive components to a substrate, most likely PCB. The ever increasing density of the SMT assembly, shrinking of component sizes and pads pitch are being driven by demands of consumer electronics, which, in turn, makes this technology highly useful for miniaturized medical devices. Teledyne supports fine pitch SMT, including 0201 case size passives, BGA and CSP packaged active devices. A range of process control and inspection equipment (profilometer, X-ray inspection, SAM, ionograph) is actively utilized to ensure conformance to IPC-A-610, Class III. Teledyne is aggressively pursuing compliance to RoHS and WEE directives. Most of the legacy and all new projects involve water-soluble solder pastes. Lead-free solder compositions are also available for qualification on specific designs, as required.

Chip & wire technology implies attachment of the unpackaged (bare) active device (die) directly to the substrate and interconnection using short pieces of thin metal wire, called wirebonds. This technique provides for a smaller device footprint on the substrate as compared to the same device in the SMT compatible package. Chip & wire is a base for ceramic hybrid technology; when the die is placed on the laminate PCB technology it is often referred to as Chip-on-Board. Depending on the substrate technology, intended conditions of use, etc., fine pitch wirebonding can be performed using either Au or Al wires, either thermosonically or ultrasonically. Since chip & wire technology was originally developed for military applications, the applicable quality provisions are governed by Mil-Std-883. In a majority of high density medical applications, chip & wire technology is being phased out and substituted by SMT. Still, chip & wire remains a viable option, if only as a way to interconnect specialty chip components into SMT compatible BGA and CSP packages. Direct chip to flex attachment using TAB bonding for sensor applications can also be implemented on the same equipment base.

Flip Chip assembly technology is an ultimate solution for any application requiring a minimum bare die footprint over the substrate. In flip chip, the die is inverted face down and aligned to the substrate such that the connection pads on the die are in registration to the respective traces of the substrate. Electrical and mechanical contact between the die and the substrate is then established by means of the additional metal pieces pre-deposited on die pads (bumps), with immediate or further reinforcement by polymer adhesive (underfill). A variety of flip chip technologies have been developed in the industry, all revolving around different techniques for electro-mechanical attachment, such as soldering, welding, and pressure contact. All these techniques require different amounts of die pre-processing and allow for different minimum pitch requirements. Flip Chip equipment and process know-how available at Teledyne covers the vast majority of the known attachment technologies, requiring both ex-situ and in-situ processes to achieve industry-leading IO densities with either solder bump or Au stud-bump interconnect. Depending on the application, flip chip attachment can be performed either directly to the main substrate or to an interposer medium, thus creating true chip-scale package (CSP) suitable for SMT processing.

Three-dimensional (3D) integration has long been considered the most advanced technique for reducing the overall size of electronic assemblies. In medical electronics this holds particularly true as the embodiments of the devices are rarely compatible with the conventional large flat motherboard architecture. The ultimate goal of 3D integration is to maximize volume density of the components of the electronic assembly, thus reducing its linear size. A variety of design concepts, from die stacking to flex folding to board interleaving can be used to accomplish the goal. There is not much art to 3D integration, other than a detailed understanding of material properties, highly controlled manufacturing processes, precision electrical and thermo-mechanical design and healthy disregard for convention.

The term optoelectronics (or photonics) refers to a wide variety of technologies and applications based on the emission or absorption of irradiated energy by semiconductor devices. Within this broad definition Teledyne Medical's expertise lies in manufacturing of high-efficiency fiber- and open-air optical sources and detectors in wavelength range from near UV to near IR. Those can be represented by pig-tailed or connectorized fiber-array modules, as well as the area LED arrays fitted with collecting, diffusing and beam-shaping optics. Fiber technology is the extension of Teledyne's know how in the field of optical communications and can be applied directly within the medical arena in modalities ranging from photodynamic therapy to interferometric pressure sensing to in-vivo spectroscopy. The primary applications of the LED arrays include high-brightness illumination and backlight systems. Teledyne designs and manufactures both standard and OEM systems and has an extensive IP portfolio available for licensing. Proprietary and patented technologies utilized in fabrication of optoelectronic assemblies are also highly instrumental in integration of the optical sensors into otherwise purely electronic device sub-assemblies.

From the standpoint of electronic assembly processes, Power and RF circuits represent more of a critical case of standard assembly rather than an art. For example, power applications traditional epoxy die attachment is customarily replaced with solder (range of Pb-Sn-Ag compounds, AuSn eutectic) attachment with subsequent wirebonding using heavy Al wire. Die attachment and wirebonding of RF components can also be tricky due to the brittleness of the component material and tough dimensional restrictions to minimize parasitic impedance. Selection of the base components and materials, layout, and thermo-mechanical phenomena affect performance of specialty assemblies greatly. One can expect to utilize odd-shaped and fragile elements (inductors, coils, antennas) requiring dedicated manufacturing steps and post-assembly tuning.

Assembly of the electronic sub-system into the final device shell is customarily performed by the device integrator. This is particularly true for long-term implants where proper welding of traditional Ti can is critical for safety and efficacy of the device. Teledyne has an extensive experience with hermetic packaging and hermeticity testing; nevertheless, it has been Teledyne Medical's policy to exclude these operations from the service portfolio for the medical device market. Assembly of the final shell not intended to be hermetic is considered a specialty, product specific operation and needs careful evaluation with respect to compatibility with Teledyne Medical standard practices and procedures.