J Fail. Anal. and Preven. (2008)8: 524-532 DOI0.10071168001741 CASE HISTORY-PEER-REVIEWED Failure Analysis on Blind vias of PCB for Novel Mobile Phones Li-NaJi· Zhen-Guo Yang·Jian- Sheng liu Submitted: 15 February 2008/in revised form: 17 August 2008/Published online: 17 September 2008 C ASM International 2008 Abstract Failure of blind via is one of the main causes of introduction an open circuit in printed circuit boards(PCBs). By using macroscopic and microscopic testing methods and char- With the expansion of high-density interconnection(HDD acterization techniques, the failure analysis of the vias on in electronic packaging technology, blind via is a newly PCB for novel mobile phones has been systematically developed type of microvia, providing electrical intercon carried out. Metallographic inspection shows obvious nection among different laminates of a printed circuit board racking along the interface of different copper layers. (PCB). Blind vias comprise electroless copper on top of Micrograph observation and chemical analysis on the grain buried interconnects formed from various kinds of copper boundary have definitely identified that inappropriate foil and underneath subsequent coatings of electroplated location of the vias concerned with circuit design and copper. Blind vias can be constructed by laser ablating the residue sulfur related to incomplete desmear process pre- holes in the top layer of the board material. Holes formed dominantly account for cracking of blind and the are then cleaned and a layer of electroless copper deposited occurrence of the cracking is caused by the formation of a in the hole, followed by coatings of electroplated copper on brittle Curs layer. Moreover, the influence of warpage top of that layer [1]. Therefore, inappropriate circuit and the reliability of the via was noted. Based on these defaults, geometry design, improper manufacturing process, and improvement countermeasures and suggestions poor plating quality can directly affect yield and electrical addressed in the paper and are of significant value for reliability of PCB. An open circuit is one of the frequent reference to the safe reliability and structural integrity of faults that occur during manufacturing [2] PCB products during manufacturing and services Blind vias play a crucial role in HDI packaging tech- nology because of their desirable electrical performance and Keywords Blind via. Cracking Sulfur embrittlement. low reflection. However, it is critical to evaluate the reli- PCB· Failure analysis ability of these structures. The technologies for manufacturing blind vias have been addressed 3, 4. The thermomechanical reliability of them is usually evaluated theoretically by experimental tests such as FEM simulation and impact tests etc [5-8]. However, comprehensive anal- LN.J·ZG.Ya yses on failure of blind vias after actual services have rarely Department of Materials Science, Fudan University been reported. Marks [9]introduced several practical failure Shanghai 200433 China cases of fip-chip packaging, but skipped the research on e-mail:zgyang@fudan.edu.cn blind vias. Also, the chemical mechanism for the cracking L-N. Ji generation in the vias has not been well studied. e-mail:lisa0119@126.com Based on our former study on failure ball grid array J-S. Liu (BGA) solder joints [10], further analysis on blind vias of China Circuit Technology (Shantou)Corporation(CCTC). the two types of PCB was carried out. Since Guangdong 515041 chir inspection is the first and important step in 2 SpringerCASE HISTORY—PEER-REVIEWED Failure Analysis on Blind Vias of PCB for Novel Mobile Phones Li-Na Ji Æ Zhen-Guo Yang Æ Jian-Sheng Liu Submitted: 15 February 2008 / in revised form: 17 August 2008 / Published online: 17 September 2008
ASM International 2008 Abstract Failure of blind via is one of the main causes of an open circuit in printed circuit boards (PCBs). By using macroscopic and microscopic testing methods and char￾acterization techniques, the failure analysis of the vias on PCB for novel mobile phones has been systematically carried out. Metallographic inspection shows obvious cracking along the interface of different copper layers. Micrograph observation and chemical analysis on the grain boundary have definitely identified that inappropriate location of the vias concerned with circuit design and residue sulfur related to incomplete desmear process pre￾dominantly account for cracking of blind vias, and the occurrence of the cracking is caused by the formation of a brittle CuxS layer. Moreover, the influence of warpage on the reliability of the via was noted. Based on these defaults, improvement countermeasures and suggestions are addressed in the paper and are of significant value for reference to the safe reliability and structural integrity of PCB products during manufacturing and services. Keywords Blind via
Cracking
Sulfur embrittlement
PCB
Failure analysis Introduction With the expansion of high-density interconnection (HDI) in electronic packaging technology, blind via is a newly developed type of microvia, providing electrical intercon￾nection among different laminates of a printed circuit board (PCB). Blind vias comprise electroless copper on top of buried interconnects formed from various kinds of copper foil and underneath subsequent coatings of electroplated copper. Blind vias can be constructed by laser ablating the holes in the top layer of the board material. Holes formed are then cleaned and a layer of electroless copper deposited in the hole, followed by coatings of electroplated copper on top of that layer [1]. Therefore, inappropriate circuit and geometry design, improper manufacturing process, and poor plating quality can directly affect yield and electrical reliability of PCB. An open circuit is one of the frequent faults that occur during manufacturing [2]. Blind vias play a crucial role in HDI packaging tech￾nology because of their desirable electrical performance and low reflection. However, it is critical to evaluate the reli￾ability of these structures. The technologies for manufacturing blind vias have been addressed [3, 4]. The thermomechanical reliability of them is usually evaluated theoretically by experimental tests such as FEM simulation and impact tests etc. [5–8]. However, comprehensive anal￾yses on failure of blind vias after actual services have rarely been reported. Marks [9] introduced several practical failure cases of flip-chip packaging, but skipped the research on blind vias. Also, the chemical mechanism for the cracking generation in the vias has not been well studied. Based on our former study on failure ball grid array (BGA) solder joints [10], further analysis on blind vias of the two types of PCB was carried out. Since visual inspection is the first and important step in failure L.-N. Ji
Z.-G. Yang (&) Department of Materials Science, Fudan University, Shanghai 200433, China e-mail: zgyang@fudan.edu.cn L.-N. Ji e-mail: lisa0119@126.com J.-S. Liu China Circuit Technology (Shantou) Corporation (CCTC), Guangdong 515041, China 123 J Fail. Anal. and Preven. (2008) 8:524–532 DOI 10.1007/s11668-008-9174-1