Substrate Surface Treatment Quality Inspection in Chip-on-Board Applications
Kähkölä, Pekka (2022)
2022
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Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:amk-202205108421
https://urn.fi/URN:NBN:fi:amk-202205108421
Tiivistelmä
Miniaturization of electronics by eliminating individual chip packages is attractive not only because of the advantage of reduction in both volume and weight but also because of the potential improvement in reliability associated with elimination of the first level of packaging at the chip. Chip-on-board (COB) technology involves mounting bare dies directly on a substrate without the need for the component’s package. Eliminating the component package reduces the required substrate area and assembly weight and removes one entire level of interconnects.
Using conventional printed circuit boards (PCBs) and standard wire bonding technology together with surface mount technology (SMT), causes COB interconnect areas to have a more apparent exposure to contamination, due to numerous process steps and logistics between production plants. The COB bonding surface is vulnerable and cannot withstand any contamination without compromising the bond reliability. For this reason, surface quality, surface finish, and process implementation and verification are paramount in defining a process for a printed circuit board assembly (PCBA) using hybrid technology i.e., COB, and SMT technology in the same configuration.
Guidelines and standards for implementing SMT or COB technology for PCB substrate can be found in several literature sources. PCBAs that incorporate both interconnect techniques are less instructed. The aim is to present the methods of both interconnect techniques and the related material-specific issues such as the selection of PCB material and surface finish. The bonding surface quality should be verified by inspections to achieve sufficient reliability between the die and the PCB substrate interconnects.
General surface quality visual acceptance criteria are presented in the PCB manufacturing level. In addition to visual acceptance criteria, destructive tests have been introduced to verify the reliability of COB wire bonding and stud bump joints. The destructive test methods and their standards for destructive tests are introduced and techniques for their cost-effective use. Practical guidance is provided on the assembly of Hybrid PCBAs. The guidance goes through material selections, PCB layout design aspects, and arranging quality controls for production.
Using conventional printed circuit boards (PCBs) and standard wire bonding technology together with surface mount technology (SMT), causes COB interconnect areas to have a more apparent exposure to contamination, due to numerous process steps and logistics between production plants. The COB bonding surface is vulnerable and cannot withstand any contamination without compromising the bond reliability. For this reason, surface quality, surface finish, and process implementation and verification are paramount in defining a process for a printed circuit board assembly (PCBA) using hybrid technology i.e., COB, and SMT technology in the same configuration.
Guidelines and standards for implementing SMT or COB technology for PCB substrate can be found in several literature sources. PCBAs that incorporate both interconnect techniques are less instructed. The aim is to present the methods of both interconnect techniques and the related material-specific issues such as the selection of PCB material and surface finish. The bonding surface quality should be verified by inspections to achieve sufficient reliability between the die and the PCB substrate interconnects.
General surface quality visual acceptance criteria are presented in the PCB manufacturing level. In addition to visual acceptance criteria, destructive tests have been introduced to verify the reliability of COB wire bonding and stud bump joints. The destructive test methods and their standards for destructive tests are introduced and techniques for their cost-effective use. Practical guidance is provided on the assembly of Hybrid PCBAs. The guidance goes through material selections, PCB layout design aspects, and arranging quality controls for production.