50μm pitch Pb-free micro-bumps by C4NP technology

Abstract

Controlled collapse chip connection new process (C4NP) is currently used in IBM manufacturing for all 300 mm Pbfree wafer bumping for flip chip packages. In this study, the extendibility of C4NP technology to ultra fine pitch applications has been explored. Reusable C4NP glass molds were fabricated and characterized for 50µm pitch application. Mold fill and wafer transfer with Pb-free solders have been demonstrated using both 200mm and 300mm wafers in a manufacturing environment. Significant improvement in bump yield was achieved for these early demonstations of fine pitch interconnections through process optimization and contamination control. Challenge in wafer inspection metrology is discussed for the 50µm pitch micro-bumps. Mechanical strength of the C4NP micro-bumps has been characterized using test dies with a full area array of microbumps.

Fluxless flip-chip bonding using a lead-free solder bumping technique

“…The cost issues in the photolithographic techniques motivated researchers to investigate alternatives. They studied the new controlled-collapse chip connection process (C4NP) [4], gang-ball placement (GBP) [5], Au-stud [6] and laser-jetting technique [7]. The C4NP and GBP are mass transfer techniques, while Au-stud bumping and laser jetting are mask-less sequential processes placing each bump individually.…”

“…Then the solder is transferred from mold to substrate in a single step. The fine pitches are more sensitive to bridging of connections but this can be avoided by using a pure N 2 atmosphere during solder transfer [4].…”

Three-Dimensional and 2.5 Dimensional Interconnection Technology: State of the Art

“…Different methods of making C4 bumps, such as masked evaporation [37], paste screening [38], and photolithographic electroplating [39], have been developed since its invention. A current C4 bumping technology developed by IBM, the C4-New Process (C4NP), has already been used in 3D chip-stacking [21,22,40]. The C4NP process utilizes a glass mold with cavities to transfer solder to the wafer.…”

“…Compared with other bumping methods, this approach combines several advantages, such as the capability of fabricating fine-pitch bumps in volume production, easy change of solder materials, environmentally friendly manufacturing (no plating chemical), low cost, etc. [40].…”