Sub-micron-accuracy Gold to Gold Interconnection Flip-Chip Bonding Approach for Electronics-Optics Heterogeneous Integration

Suzuki

et al. 2013

Jpn. J. Appl. Phys.

High-precision integration has valuable meaning in heterogeneous convergent technology. In this paper we report on a new high-precision low-temperature bonding approach, capable of submicron alignment accuracy, based on the conventional ultrasonic flip-chip bonding technique and modified metal pad and bump elements. The interconnection pair made from a conductive-sloped hollow bonding pad (concave) and metal cone bump (convex) elements, i.e., misalignment self-correction elements, helps in aligning and maintaining the alignment between the chip and the substrate during stacking. By this method, the stacking accuracy can be improved significantly and effectively. Repeatable submicron (i.e., less than 500 nm) bonding accuracies are confirmed through experimental investigation. Moreover, reliable bond characteristics including electrical and mechanical properties are observed, validating the performance of the bonding approach. With these results, the proposed high-precision low-temperature bonding approach shows its suitability for heterogeneous electronics–optics integration applications.

Section: (A)mentioning

confidence: 99%

“…Therefore, our work deals with effectively maintaining the alignment between the chip and the substrate during stacking in order to obtain submicronrange precision bonding, at a low temperature, using the thermosonic technique and modified bonding pad and bump elements. 25) 2. Bonding Approach Using Misalignment Self-Correction Elements…”

Section: Introductionmentioning

confidence: 99%

Sub-Micron-Accuracy Gold-to-Gold Interconnection Flip-Chip Bonding Approach for Electronics–Optics Heterogeneous Integration

Suzuki

et al. 2013

Jpn. J. Appl. Phys.

“…In our previous works, we have succeeded in making reliable 10 μm-diameter Au bump interconnections at room temperature, with submicron range bonding accuracy [13,14]. Copper, due to its superior electrical conductivity, superior electromigration resistance, lower cost, as well as superior mechanical properties, such as yield stress and Young's modulus, is preferred over Au to form electrically and mechanically compliant interconnect elements [15][16][17].…”

Section: Introductionmentioning

confidence: 99%

Modified thermosonic flip-chip bonding based on electroplated Cu microbumps and concave pads for high-precision low-temperature assembly applications

Suzuki

2013 IEEE 63rd Electronic Components and Technology Conference

et al. 2013

Thermosonic flip-chip bonding (TS-FCB) is known as a technique suitable for low-temperature bonding and has been used in many integration applications. In this paper, a modified TS-FCB based on microbumps and concave pads, is presented. Electroplated Cu microbumps, and etched invertpyramid-shape bonding pads are used to enhance the bonding accuracy of the conventional TS-FCB technique. Experimental validation of the bonding approach is conducted. Reliable bonds, with significant increase in the post-bond accuracy, i.e. within 1 μm range in in-plane offsets, are obtained at 120 ºC using the proposed bonding approach. These achievements illustrate the ability to use this approach for highprecision low-temperature converging applications. IntroductionThe flip-chip bonding (FCB) with thermal compression method has been a promising technique for high density interconnection while only needing a simple process. Generally, the post-bond accuracy of presently commercialized FCB machines has been limited to the range of 2 μm -5 μm, because of unavoidable effects such as thermal-induced misalignment caused by thermal expansion mismatching between the bonding chip and substrate, and by horizontal shifting of the press tool due to the shear force generated from the large down force during pressing. For emerging demands, such in photonics-electronics convergence system technology -PECST (Figure 1), the optical performance of a system is highly dependent on the coupling efficiency which is mainly affected by assembly deviations [1][2][3][4]. Therefore, the integration accuracy of the FCB approach needs to be improved significantly in order to realize low power consumption, highspeed, high-performance photonics-electronics systems.The improvement of integration accuracy is being investigated by several research groups [4][5][6][7][8][9]. Attempting to improve the alignment accuracy of the FCB method through increasing the resolution of the alignment stage motion and increasing the magnification of the IR image camera is not sufficient for high-precision bonding. Additionally, highprecision alignment systems have high costs, as well as very long process times. The key point to achieve high-precision bonding results is to maintain the alignment of the chip and the substrate during the bonding process [10][11][12].In our work, the integration accuracy is effectively improved by means of maintaining the alignment between the chip and substrate during bonding, aiming at sub-micron range precision, at an acceptably low temperature. In our previous works, we have succeeded in making reliable 10 μm-

“…In our study, we proposed a high-precision room-temperature bonding approach, capable of achieving submicron post-bond alignment accuracy, based on the ultrasonicassisted thermo-compression FCB technique and self-aligned interconnection pairs. [26][27][28][29] The conventional bump/planarpad interconnection [Fig. 2(a)] was modified to form concave-convex self-aligned structures: a truncated inverted pyramid (TIP) bonding pad and a micro bump [Fig.…”

Section: Introductionmentioning

confidence: 99%

15-µm-pitch Cu/Au interconnections relied on self-aligned low-temperature thermosonic flip-chip bonding technique for advanced chip stacking applications

Watanabe

et al. 2014

Jpn. J. Appl. Phys.

In this paper, we report the development of reliable fine-pitch micro bump interconnections that used a high-precision room-temperature bonding approach. The accuracy of the bonding process is improved by modifying conventional bump/planar-bonding-pad interconnections to form self-aligned micro bumps/truncated inverted pyramid (TIP) bonding pads, i.e., misalignment self-correction elements (MSCEs). Thermosonic flip-chip bonding (FCB) is utilized to form reliable bonds between these MSCEs at acceptable low temperatures. By applying the proposed bonding approach, the demonstration of fine-pitch Cu bump to Au bonding pad interconnects chip stacking has been realized. Microstructure analyses reveal that 15-µm-pitch micro bump joints are fabricated at room temperature.