Surface Mount International Conference Proceedings


Author: Per Carlsson
Company: IVF
Date Published: 9/10/1996   Conference: Surface Mount International

Abstract: This paper gives an overview of a four layer build-up (SBU) process using a standard printed wiring board (PWB) technology. The sequential multilayer main aim was to generate small vias in the order of 100 pm in a conventional photo definable two component solderresist by normal UV exposure and developing. The conductors were then built by plating copper using conventional electroless and electrolytic plating. The solder lands were plated with electroless nickel and gold. The SBU process on an FR-4 substrate is apt to achieve high density. Considering the reliability, the characteristics of continuity and isolation are important. In this paper, a continuous reliability, insulator and via reliability are discussed. The electrical reliability testing consisted of @ace insulation resistance (SIR) measurements at elevated temperature and humidity (85°C/85% RII). The crack formation in vias and conductors between layers was tested by daisy chain structures at prolonged temperature cycling. Using this method, the effect of various materials and processes on electrical reliability were adequately tested. In the temperature cycling the temperature was ramped between -40°C and 100”C. The cycle time was one hour. The boards manufactured in the study were tested in temperature cycling for over 2,000 cycles without any failure. However, the SIR values were rather low and the adhesion between the copper and the top layer of the dielectric was 25% lower than conventional PWB. Keywords Stiace laminar circuits, sequential build-up boards, blind vim, reliability

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