Fine pitch area array packages are often assembled to flexible printed circuit boards, which require numerous low-frequency mechanical deflections. The interconnect package reliability emphasis has become focused more on isothermal bending fatigue. The interconnect failures due to bending fatigue were found to be different than those which occur if the packages were subjected to accelerated temperature cycling. A test method has been developed to evaluate isothermal mechanical bending fatigue reliability of area array packaging. Mechanical fatigue results of 1.0, 0.8, and 0.75 mm pitch packaging will be presented, demonstrating the effect of package substrate material properties on fatigue life and fracture morphology. Numerical finite element analysis results will also be presented to support and expand the findings in this study.

Capillary flows of dense, model suspensions and industrial underfill encapsulants are investigated. Flow behavior is characterized by measuring the infiltration rate of an encapsulant or model suspension into a channel formed by parallel surfaces. A capacitance measurement technique is used to track the advancement of the front. Significantly this technique allows the channel surfaces to be formed from opaque materials such as those that found in the principal industrial application of electronics packaging. A scaling law to describe the functional dependence of the front position on channel spacing, surface tension and viscosity is presented.

An immersion plating process using organic solutions was used to deposit a seed layer of copper and to activate the surface of thin film aluminum surfaces and bond pads. The seeded surfaces were subsequently electroless copper plated and tested for compatibility with soldering assembly. It was demonstrated that the copper particles deposited from the organic solution onto sputter deposited aluminum thin films were able to act as nucleation sites for the subsequent build up of adherent, continuous copper films from conventional electroless plating baths. In addition, the metal deposition from organic solution process was found to be very selective on patterned test vehicles and integrated circuits as metal deposition occurred only on the exposed aluminum bond pads and not on any passivated surfaces. Tests were conducted to determine the solderability of the samples after only seeding in the organic solution as well as the combination of seeding plus electroless copper deposition. In these tests, all attempts to directly solder without any pre-treatment were unsuccessful. Results on solder adherence varied with different substrates. Nevertheless, the concept of depositing metal seed layers in these applications is feasible. Additional work is needed, however, to optimize the deposition process for each particular surface to be soldered.

The paper describes a low temperature bond process based on an oxygen plasma pretreatment followed by 200°C and 400°C annealing which was to be integrated in our technological process flow to produce micromechanical devices in bulk and surface micromachining like acceleration sensors, gyroscopes and mirror arrays [1]. The results of infrared transmission and the measured bond strengths of the prepared test wafers will be presented in dependence on various pre-treatments and annealing times as well as temperatures. First die separation tests as well as additional detailed investigations showed that the bonding process has the potential to replace an anodic bonding process. During the development of the low temperature bond process it was shown that it is possible to reach a bond strength between 1.5 J/m2 and 2.8 J/m2 depending on the annealing conditions. To optimize the necessary size of the bond frame and to quantify the bond strength limits of the process a test pattern was designed with different arrangements of sensor structures like bond frames, spaces and chevron notch structures. The investigation showed the achieved bond yield in dependence on different sensor structures and bond conditions.