Effects of Intense Pulsed Light Energy on Metallurgical Properties of Cu Pillar Joints

Conventional reflow soldering, which has been mainly used, has a critical disadvantage in that electronic components undergo thermal damage and thermal deformation due to long processing time. To improve these problems, intense pulsed light (IPL) soldering, a next-generation bonding process that can be bonded in a very short time by irradiating multi-wavelength light, was proposed. In addition, as the size of the bump decreases due to the high-integration of semiconductor packages, the volume fraction of intermetallic compound (IMC) formed at the joint interface increases rapidly due to the limited amount of solder. Since thick IMCs have a negative impact on joint reliability, active research has been conducted to prevent the growth of IMCs. In this study, the properties of the Cu pillar joint were evaluated after the soldering process using IPL energy. The results were reported by comparing the bonding interface properties with the conventional reflow soldering with a long process time. And the effect of the presence of Ni layer at the interface of Cu pillar/solder on the bonding interface was compared and analyzed. After IPL soldering with a short process time, a very thin IMC was formed at the solder cap/Cu pillar interface. And the thickness of the IMC increased as the IPL number increased from 30 to 50. In addition, Cu<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf>Sn<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> IMC was formed in the CS structure (Cu pillar/solder), and (Ni,Cu)<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>Sn<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> IMC was formed in the CNS structure (Cu pillar/Ni layer/solder) in which the Ni layer was inserted.