Nanoparticle silver (NPS) conductors are increasingly being investigated for printed electronics applications. However, the adhesion mechanism of the nanoparticle silver to substrate materials has not been identified yet. In particular, the adhesion of NPS to organic materials such as the widely used polyimide Kapton HN and Kapton FPC dry films is concerned with low adhesion strength because the processed polymer surface is chemically inert. Moreover, its adhesion to substrate materials such as benzocyclobutene (BCB), copper and aluminum was found to be very weak. Therefore, in this paper, the mechanisms of NPS adhesion to organic and inorganic materials are identified as the first step in improving NPS adhesion strength. Improving the adhesion strength of NPS will be the key issue for printed electronics applications. The adhesion of NPS to substrate materials was found to be mainly attributed to van der Waals forces based on particle adhesion mechanisms. This finding provides the initiative of developing an adhesion prediction model of NPS to substrate materials in order to provide guidelines for improving the NPS adhesion strength to the substrate materials used in printed electronics.

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Rapid package prototyping (RPP) technology based on a data-driven chip-first approach using nano-particle silver (NPS) interconnects has been developed to promptly assess novel package designs, new packaging materials, and performance of new devices. A potential limitation of rapid package prototyping with NPS interconnects is the adhesion between NPS and polymer substrates such as LCP, Polyimide, and BCB. Improving the adhesion strength of NPS is a key issue for reliable package prototypes with NPS interconnect. Qualitative measurement of the adhesion strength of NPS is necessary to investigate the adhesion improvements of NPS. A new adhesion test method is developed to estimate the interfacial fracture energy of NPS films. It has been found that most of the existing adhesion test methods are not directly applicable to NPS films. The newly developed adhesion test method is called Modified Button Shear Test (MBST) because it modifies the conventional button shear test and integrates the generally known die shear test. The MBST is used for measuring the interfacial fracture energy of NPS interconnect material. The interfacial fracture energy varies depending on physical, mechanical, and chemical states of the interface between NPS and polymer substrates. A mechanical interlocking adhesion model [7] will be validated using MBST to demonstrate that the contribution of surface roughness to the interfacial fracture energy can be identified. It will show that the Yao's model is an applicable mechanical interlocking model for NPS film adhesion model.

In order to reduce process complexity, manufacturing cost and lead time, while enhancing electrical and mechanical reliability performance, a new innovative approach, which specifically targeted to prototype and low volume production in micro-systems packaging and system in package, is being developed. The approach is rapid prototyping of microsystems packaging by data driven chip-first packaging process using nanoparticle metal colloids. According to the concept of the chip-first process, bare dice and standard passive components are first embedded into a carrier substrate to achieve a common, planar surface. On the planar substrate, polyimide film is laminated to make a dielectric layer. Over the dielectric layers and chip metal pads, silver nano-particles, which has high conductivity and good adhesion to copper, polyimide, benzocyclobutene (BCB) and liquid crystal polymer (LCP), are deposited by screen printing, forming a three dimensional electrical circuit. This approach is datadriven so that it requires no photo masks and reduces turnaround time and is also less limited by substrate composition and morphology. This approach also eliminates the need for special chip processing such as the need required for flip chip solder bumps and permits using any chip technology and any chip supplier allowing mixed devices. In addition, the datadriven process with metallic nanoparticle avoids the extreme processing conditions required for standard IC fabrication such as wet chemistry processing and vacuum sputtering. Nano-particles typically measure around 5nm in diameter and can be sintered at plastic-compatible temperatures as low as 220C to form material nearly indistinguishable from the bulk material. These results represent an important step to a system packaging characterized by high density, low cost, and datadriven fabrication for rapid turn-around time.