Nano‐ and micro‐filled conducting adhesives for z‐axis interconnections: new direction for high‐speed, high‐density, organic microelectronics packaging

Abstract

PurposeThe purpose of this paper is to discuss the use of epoxy‐based conducting adhesives in z‐axis interconnections.Design/methodology/approachA variety of conductive adhesives with particle sizes ranging from 80 nm to 15 μm were laminated into printed wiring board substrates. SEM and optical microscopy were used to investigate the micro‐structures, conducting mechanism and path. The mechanical strength of the various adhesives was characterized by 90° peel test and measurement of tensile strength. Reliability of the adhesives was ascertained by IR‐reflow, thermal cycling, pressure cooker test (PCT), and solder shock. Change in tensile strength of adhesives was within 10 percent after 1,000 cycles of deep thermal cycling (DTC) between −55 and 125°C.FindingsThe volume resistivity of copper, silver and low‐melting point (LMP) alloy based paste were 5 × 10−4, 5 × 10−5 and 2 × 10−5 Ω cm, respectively. Volume resistivity decreased with increasing curing temperature. Adhesives exhibited peel strength with Gould's JTC‐treated Cu as high as 2.75 lbs/in. for silver, and as low as 1.00 lb/in. for LMP alloy. Similarly, tensile strength for silver, copper and LMP alloy were 3,370, 2,056 and 600 ψ, respectively. There was no delamination for silver, copper and LMP alloy samples after 3X IR‐reflow, PCT, and solder shock. Among all, silver‐based adhesives showed the lowest volume resistivity and highest mechanical strength. It was found that with increasing curing temperature, the volume resistivity of the silver‐filled paste decreased due to sintering of metal particles.Research limitations/applicationsAs a case study, an example of silver‐filled conductive adhesives as a z‐axis interconnect construction for a flip‐chip plastic ball grid array package with a 150 μm die pad pitch is given.Originality/valueA high‐performance Z‐interconnect package can be provided which meets or exceeds JEDEC level requirements if specific materials, design, and manufacturing process requirements are met, resulting in an excellent package that can be used in single and multi‐chip applications. The processes and materials used to achieve smaller feature dimensions, satisfy stringent registration requirements, and achieve robust electrical interconnections are discussed.

Conductive Polymer Composites

“…Morphological studies showed that the decreased resistivity was the result of sintering of Ag nanoparticles within the polymer matrix. Das and co-workers developed Ag-based nano-and micro-filled conductive adhesives for z-axis interconnections (87). It was found that with increasing curing temperature, the resistivity of the Ag-filled paste decreased due to sintering of the metal particles.…”

Three-dimensional multi-layer through-hole filling properties of solderable polymer composites with low-melting-point alloy fillers

“…The processing costs of via-hole filling and interlayer interconnection account for about 70 % (via-hole filling: about 40 %, interlayer interconnection: about 30 %) of the overall production cost for the 3D package. To overcome the limitations of the conventional Cu electroplating technique, several via-hole filling techniques have been reported that use different conductive materials (e.g., solder material [12,13] or a conductive adhesive [8,14,15]). However, these via-hole filling techniques do not eliminate or simplify the interlayer interconnection process because these studies focused on via-hole filling for individual device wafers.…”

Joints realized by sintering of pressureless Ag paste

“…A nanoscale pressureless silver paste was developed for replacing a pressure assisted micro-sized silver paste as well (Chou et al, 2017). Application of pressure during the paste sintering puts increased demands on production in the industry automation (Das et al, 2008;Felba, 2018;Göbl, 2009). In addition, the damage of electronic components occurs during the sintering process (Zhang et al, 2012).…”