IMS (Injection Molded Solder) Technology with Liquid Photoresist for Ultra Fine Pitch Bumping

Abstract

IMS (injection molded solder) is an advanced solder bumping technology with solder alloy flexibility even at very fine pitch and small size. One of key materials for successful fine pitch bumping by IMS is a photoresist material. The photoresist material must be stable at high temperature during the IMS process and be perfectly stripped after the IMS process without any residue on the surface of the substrate. In this study, negative tone liquid photoresist materials were prepared to investigate effects of thermal cure of photoresist on IMS process and stripping performance. With appropriate cure conditions, successful bumping without any film damages at IMS process and any residue at stripping was achieved. Fine pitch bumping down to 40 μm pitch with 20 μm diameter was demonstrated with a Sn-3.0Ag-0.5Cu solder. Also physical and electrical connections for the solder joints of IMS bumps to Ni/Au pads were confirmed using a 80 μm pitch test vehicle.

Development of Liquid Photoresist for IMS (Injection Molded Solder) with High Thermal Stability

“…As described in the previous paper, solder bumps with a diameter between 20 μm and 75 μm were successfully obtained by IMS technology, using PR-1 pre-baked at 200°C for 10 minutes as a photoresist mask [11]. However, the solder filling rate has to be 100% in order to be applied widely in industrial use.…”

“…Therefore, novel bumping processes are required to satisfy the variety of recent requirements for high I/O density, fine bump pitch, novel solder bump composition, and further process cost reductions. Recently, a promising bumping process called "IMS (Injection Molded Solder)" was proposed [6][7][8][9][10][11]. In this process, molten solder is directly injected into holes patterned in photoresist mask films, instead of carrying out conventional electroplating.…”

Design and Implementation of Solder Paste Dispenser Based on Linear Drive System

“…Following from previous research in pneumatic solder paste dispenser has a problem such as a pressure drive system affected by heat, humidity, air pressure fluctuations, changes in viscosity. It can weaken the ability of the dispenser to eject the liquid solder paste on the surface of the PCB (Printed Circuit Board), particularly in SMD (Surface Mount Device) [7] .…”

Development status of photoresist as mask material for Injection Molded Solder (IMS) technique

“…However, novel bumping processes are required to satisfy the variety of recent requirements for high I/O density, fine bump pitch, novel solder bump composition, and further process cost reductions. Recently, a promising bumping process called "Injection Molded Solder (IMS)" was proposed [6][7][8][9][10][11] . In this process, molten solder is directly injected into holes patterned in photoresist mask films, instead of carrying out conventional electroplating.…”