New liquid crystal polymer (LCP) flex circuits to meet demanding reliability and end-use applications requirements
Flex circuits made from LCP, a thermoplastic polyester, use a newly developed, adhesiveless, roll-to-roll process flow similar to that used for polyimide substrate, including vacuum metallization, additive plating and chemical etching of dielectric. Critical dimensions for both LCP raw test circuits and LCP-coverlayer-laminated LCP test circuits from multiple lots met the specification established for polyimide circuits. LCP circuits have also proven to be dimensionally stable at elevated temperature in common post-circuit operations including die attachment, wire bonding, encapsulation and solder reflow. Trace adhesion was not degraded after solder immersion at 280°C. Wire bonding has proven to be as straightforward as on polyimide, yielding strong wire bonds in a large process window. Integration studies with other materials such as LCP coverlayers and soldermasks that could enable a wide variety of product constructions with multiple materials are going forward. Initial parts passed the entire battery of reliability tests that included moisture resistance, thermal shock and temp-humidity-bias stressing to enable the definition of preliminary process conditions for a wide variety of soldermasks with different polymer chemistries. LCP-based flex circuits should have extended applications beyond those for existing polyimide offerings, due to their reduced moisture uptake and coefficient of humidity expansion and better electrical properties, particularly dissipation factor. These applications include liquid crystal display module (LCDM), medical, high frequency applications, high-density disk drive and integrated circuit packaging.
Highly Accelerated Temperature and Humidity Stress Test Technique (HAST)
A method for highly accelerated bias-temperature humidity stress testing is described. This method allows testing in the regime 100°C/175°C and 50% R.H./85% R.H. Experimental results which demonstrate invariance of corrosion failure modes and lognormal sigmas under different high temperature-humidity conditions are presented. Acceleration factors relative to 85°C/81% R.H. and 60°C/81% R.H. stress tests are given.
A New Vacuum Pressure Infiltration CFRP Method and Preparation Experimental Study of Composite
In order to prepare a carbon-fiber-reinforced polymer composite (CFRP) with ideal microstructure and properties, a new vacuum pressure infiltration CFRP method is proposed based on an analysis of existing CFRP preparation process methods. Research on composite material preparation systems was carried out by using this new method principle. The system mainly includes a fiber pre-forming module, a vacuum heating infiltration module, a hot-press curing molding module, and a data acquisition control module. Under the conditions of natural curing at 0 MPa + 6 h + 25 °C, vacuum heating curing at –0.05 MPa + 30 min + 80 °C, and hot-press curing at 0.7 MPa + 5 min + 50 °C, a two-dimensional (2D) CFRP with excellent microstructure and properties was successfully prepared. Observing the microstructure of the prepared composite material, it can be found that the inside of the composite material was sufficiently and uniformly infiltrated, and common preparation defects such as holes and delamination were effectively controlled. Through the performance test, the bending strength of the material reached 790 MPa.