Hunter Chan

Through-package-via formation and metallization of glass interposers

Interposer technology has evolved from ceramic to organic materials and most recently to silicon. Organic substrates exhibit poor dimensional stability, thus requiring large capture pads which make them unsuitable for very high I/Os with fine pitch interconnections. Therefore, there has been a trend to develop silicon interposers. Silicon interposers however, suffer in two ways; 1) they are expensive to process due to the need for electrical insulation around via walls, and 2) they are limited in size by the silicon wafer from which they originate. In this paper, glass is proposed as a superior alternative interposer technology to address the limitations of both silicon and organic interposers. The inherent electrical properties of glass, together with large area panel size availability, make it superior compared to organic and silicon-based interposers. Glass however, is not without its challenges. It suffers in two ways: 1) formation of vias at low cost, and 2) its lower thermal conductivity compared to silicon. This research explores glass as an interposer material, and addresses the above key challenges in through package via (TPV) formation and subsequent low cost and large area metallization to achieve very high I/Os at fine pitch.

Chip-last embedded actives and passives in thin organic package for 1–110 GHz multi-band applications

This paper presents for the first time a novel manufacturing-compatible organic substrate and interconnect technology using ultra-thin chip-last embedded active and passive components for digital, analog, MEMS, RF, microwave and millimeter wave applications. The architecture of the platform consists of a low-CTE thin core and minimum number of thin build up organic dielectric and conductive layers. This organic substrate is based on a new generation of low-loss and thermally-stable thermosetting polymers (RXP-1 and RXP-4). Unlike LCP- and Teflon-based materials, the RXP material system is fully compatible with conventional FR-4 manufacturing processes. Ultra-thin silicon test die (55µm thick) has been embedded in a 60µm deep cavity with a 6-metal layer RXP substrate and a total thickness of 0.22mm. The embedded IC is interconnected to the substrate by ultra-fine pitch Cu-to-Cu bonding with polymer adhesives. This novel interconnection process performed at 180°C, has passed 1,000 thermal shock cycles in reliability testing. Because of manufacturing process simplicity and unparalleled set of benefits, the chip-last technology described in this paper provides the benefits of chip-first without its disadvantages and thus enables highly miniaturized, multi-band, high performance 3D modules by stacking embedded 3D ICs or packages with embedded actives, passives and MEMS devices.

Design and fabrication of bandpass filters in glass interposer with through-package-vias (TPV)

This paper presents the integration of WLAN (2.4 and 5GHz) bandpass filters in glass interposer using through-package vias. The filters include novel embedded passive components such as stitched capacitors with reduced shunt parasitics and via-based inductors that provide area reduction. The filters designed for 2.4 GHz showed an insertion loss of less than 2dB and better than 15dB return loss, while the 5GHz filters showed an insertion loss of less than 1dB with better than 20dB return loss. Stop-band rejection of over 35dB was observed at 2.2 GHz on the 2.4 GHz bandpass filters. The measured results showed good agreement with the simulated values and indicated that the performance on glass interposer closely matches the performance of the more expensive high resistivity silicon with similar properties.

Ultra-high density, thin core and low loss organic system-on-package (SOP) substrate technology for mobile applications

In this paper we present an ultra-high wiring density build-up substrate targeted at 30µm IC-to-substrate interconnect pitch, using a new low loss thin core laminate (RXP-1) and low dielectric constant and low loss thin build up dielectric (RXP-4). The RXP-1 core is a glass fiber reinforced organic laminate with a thickness in the range of 50–110µm. The RXP-1 core has a stable dielectric constant of 3.25 and loss tangent of 0.004 at 1–40GHz. The RXP-4 build-up film has a stable dielectric constant ≪3, a loss tangent of 0.004 at 1–40GHz [1] and a film thickness of 10–25µm. A process test vehicle having a 4-metal layers structure (1+2+1) was designed for process development and reliability characterization. The total thickness of the completed 4-metal layer substrate demonstrated was 160µm. The substrate design rules include a minimum copper line width and space of 15µm, blind microvia diameter of 25µm and through hole diameter of 50µm. Line width and space of 10µm and through hole diameter of 30µm was also designed for testing the process limits. Preconditioning test, 3X lead-free reflow and thermal shock (−55∼+125°C, air-to-air) test up to 1,400 cycles showed that the new low loss thin dielectric film and thin core organic system is reliable. This substrate can be used for high speed systems, low profile thin packages, portable devices, mobile applications, system-in-package (SiP) and system-on-package (SOP).

Characterization of Next Generation Thin Low-K and Low-Loss Organic Dielectrics From 1 to 110 GHz

This paper presents, for the first time, characterization results of next generation dielectric core and build up material called RXP, which has low dielectric constant (2.93-3.48) and low loss tangent (0.0037-0.006) up to 110 GHz. Unlike LCP, this material can be made ultra-thin with low processing temperature and is ideally suited for mobile applications. Causal models suitable for high frequency applications have been extracted by measuring the response of cavity resonators using vector network analyzer and surface profiler.

Filter integration in ultra thin organic substrate via 3D stitched capacitor

This paper presents filters integrated in ultra thin multilayer organic substrate using 3D stitched capacitor alleviating shunt parasitics and providing tunable capacitors. Insertion loss of less than 2.2dB, return loss of greater than 15dB at 2.4 GHz and attenuation of greater than 30dB below 2.0 GHz and at 4.7 GHz were measured. The measured results showed good agreement with simulated results. This paper demonstrated 2.4 GHz bandpass filters with size of 2.2mm × 3.0mm × 0.2mm (1.2mm3) in ultra thin organic RXP substrate.

A compact third-order 5 GHz bandpass filter with enhanced stopband characteristics in ultra thin organic substrate

A lumped-element bandpass filter based on new RXP ultra-thin organic technology with enhanced stopband rejections is proposed in this paper. The design is based on a third-order capacitively-coupled resonator circuit with unique resonator and ground inductor. For demonstration of the proposed circuit and RXP technology, a 5 GHz bandpass filter has been implemented in a four-metal layer 0.191 mm thin RXP substrate. The measured results have a good agreement with the simulation and show that insertion loss is less than 1.24 dB with larger than 1 GHz bandwidth and sharp rejections at both low and high stopband.

Adhesion and RF properties of electrically conductive adhesives

Adhesives used for mechanical bonding and electrical/thermal transport in high performance electronic packages require high adhesion strength and electrical properties at elevated temperatures. Adhesion strengths of electrically/thermally conductive adhesives on Ni, Cu and Sn surfaces at room temperature and elevated temperature (100 °C) were studied. Their high temperature adhesion strengths on those metal surfaces were improved by surface pretreatment with an adhesion promoter (AP). The Tg > 100 °C and the low coefficient of thermal expansion (CTE) of the ECA help maintain the low thermal coefficient of resistance (TCR) at 100 °C similar to that of bulk silver. High frequency properties of the ECA at an elevated temperature are presented and show great stability of the insertion loss in the 1 to 8 GHz frequency range. Also, the ECA shows good high frequency performance compared with Cu.

Chip-package electrical interaction in organic packages with embedded actives

System integration and miniaturization needs are the driving factors for embedding active and passive components within packages. But embedding components also results in unwanted interferences within the package. This paper demonstrates chip-package interaction in the form of electromagnetic interference between the embedded chip and its package. The electromagnetic coupling experienced by the bond-pads of the embedded chip, the effect of bulk substrate of the embedded chip on the coupling across the package and the influence of die to cavity clearance on the vertical electromagnetic coupling across the different layers of the package housing the embedded chip are analyzed. Results from simulations and measurements are presented to demonstrate the phenomena studied.