Formula Development for Through-Hole Filling by Copper Electroplating

• Main Authors: Jhih-Jyun Yan, 嚴之君
• Other Authors: Wei-Ping Dow
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/eq45q9

碩士 === 國立中興大學 === 化學工程學系所 === 101 === In modern life, people are using electronic products that are light, thin, short, small, multifunctional and communication-rapid. To achieve this goal, electronic devices that have narrow line widths and high density interconnect (HDI) are being vigorously developed. IC chip packaging will benefit from two-dimensional connection turning towards three-dimensional stacking technology. However, the volume shrinkage in electronic devices results in a high aspect of conducting through-holes that are used as the message channels. The high aspect ratio through hole renders current density distribution in the hole and at the hole mouth to be not uniform during copper plating, which increases difficulty in copper superfilling of through holes. For this reason, many people added chemical additives in the copper plating solution, but the more additives in the plating solution, the more complicated mechanism in the copper plating. Regarding plating additives, leveler usually is the organic heterocyclic compound (Azole Compound) that has a quaternary ammonium (R4N+). Leveler can prevent copper ions from fast reduction and deposition at the hole mouth where the current density distribution is high; the organosulfide additives, also known as accelerators and referred to as brighteners, enable rapid copper deposition. In addition, acids are often added as supporting electrolytes to reduce the resistance of the plating solution and to avoid a side reaction of hydrogen generation at the cathode; the chloride ions play a catalytic role in the copper plating bath. In this work, I first used leveler and chloride ion and adjusted acid concentration with a simple formulation to fill the through hole in the butterfly filling mode. According to past experience, only three additives can perform copper superfilling of a through hole in the absence of acid, but there are cracks in the copper deposition. If 0.54M sulfuric acid is present in the plating solution, then the deposited copper structure is improved but precipitate is also produced in the plating solution. In this work, organic acids were employed solve these problems, copper cracks and plating solution precipitation. A single additive combining with organic acid can fill up the through-hole. On the other hand, the PCB sample was put in a pre-dip bath containing an organosulfide and plated in a plating bath containing leveler and chloride ions to obtain a novel plating mechanism for filling the through-hole. Copper was preferentially deposited at the center of the through hole, but it is different from the butterfly filling mode. The copper deposition profile is not like butterfly wings but a plug stuffed in the center of the hole. The plate surface and the hole mouth portion did not have copper deposition. After copper filling, no V-shaped recess remained on the hole opening portion, forming a very thin surface copper layer on the PCB sample. This is referred to as H-type filling technique.