Using Copolymers as Suppressors in a Copper Plating Bath for Through-Hole Filling

• Main Authors: Shih-I Wen, 温士誼
• Other Authors: Hou-Chien Chang
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/87955085711212260561

碩士 === 國立中興大學 === 化學工程學系所 === 104 === About the through-hole (TH) metallization, to meet the recent requirement of a dense circuit design, the traditional plated through-hole (PTH) is replaced by TH filling plating with copper, which improve the reliability issue caused by resin plug process. However, the geometry of TH cause concentrated current density distribution at the hole mouth, increasing difficulty in TH filling and resulting in a void formation. By using accelerator, suppressor and leveler as plating additive in the copper plating bath, the Butterfly Technology (BFT) was developed to achieve a void-free filling of a through-hole. However, the BFT for TH filling cause an issue of thick copper layer on the PCB surface and the large dimple on the hole mouth, which lead to difficulty in following stacking steps between two layers. Literature has mentioned that triblock copolymers, polymerize by ethylene glycol and propylene glycol, have strong suppression on copper electroplating than common used poly(ethylene glycol) (PEG). The strong suppressor can minimize surface copper thickness to achieve excellent filling performance. In this study, we introduce a copper filling formula to perform the through-hole filling. Triblock copolymers were employed as suppressors to replace PEG and developed new formula for TH filling. By comparing the through-hole plating experiments and the electrochemical analysis, the relationship between interaction of additives and TH filling were investigated. Relative to using ethylene glycol as a suppressor, the Chronopotentiometry and Cyclic voltammetry results show that using triblock copolymers as suppressors are beneficial to form the difference of deposition rate between hole surface and hole center. And the TH filling has been achieved by using triblock copolymers as suppressors with small amount leveler or without leveler. Corresponding to the plating results, the difference of deposition rate can promote the deposition of copper ions at the hole center preferentially that a thin copper layer is obtained on surface after TH filling and the through-hole is filled without dimple. But the curvature enhance and accumulation of accelerator leads to a copper bump shape deposition.