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|Advanced Adhesion Promotor Systems For IC Substrate Packaging|
|Keywords: Adhesion, Dielectric, Soldermask|
|In the manufacture of IC substrates the additive production process route results in the joining together of different materials. One example of this would be in the bonding of a structured core layer containing copper traces, with the next build up layer of dielectric material; another case would be in the application of a solder mask material to the finished substrate build. In both of the examples quoted, typical ways to arrive at suitable adhesion between different materials would be to roughen one of the surfaces. This is most commonly achieved by etching the structured copper traces to produce a strong mechanical bonding between the subsequent layers. However this mechanism of etching the copper traces to achieve surface roughness can create a number of very specific problems. First as copper features get ever smaller it is not desirable to etch away this structured copper as this can result in a form of dimensional instability. Secondly, we should also consider the influence of a roughened copper surface upon electrical performance of the device, especially in the case of high frequency applications where the path of the electrical signal moves into the outer most skin of the copper track. If the outer layer of the copper track is heavily roughened this will effectively create a barrier for the path of the signal. The result of such roughness is a high and unacceptable signal insertion loss. The ideal way to overcome these issues would be to use a bonding enhancement system which provides the minimum possible surface roughening. However the challenge here is that any such low roughness system must still offer the best possible bond integrity and functional performance in combination with low signal loss to be compatible with high frequency applications. This paper highlights the development of a low etching treatment process which meets all of the challenges of Enhanced functional performance together with lowest signal insertion loss to be suitable for so called 5G applications. EXPT NovaBond EX is a system developed to meet these challenges, with the formation of a smooth copper surface with minimal copper loss (less than 200-nm), which is subsequently treated with a coating of adhesion promotor to provide the strongest possible bond strength.|
|Neal Wood, Global Prouct Marketing Manager