No-clean assembly process conditions-effects on flip-chip/underfill reliability

No-clean flux chemistries are gaining acceptance in many high volume SMT manufacturing processes worldwide. These materials offer advantages in manufacturing efficiencies by reducing overall manufacturing cycle time and reducing in-process inventories. The use of no-clean flux materials also eliminates potential environmentally dangerous cleaning solvents from the manufacturing environment (McCurdie, 2000). Dozens of no-clean flux formulations are now available from leading manufacturers based on both natural and synthetic chemistries. The impact of these materials, however, on product reliability must be assessed prior to acceptance. No-clean flux residues have been shown to affect, for example, the physical properties of epoxy underfill materials (Bacher and Kirkpatrick, 1999) as well as the long-term reliability characteristics of flip-chip assemblies (Todd, 2000). A series of experiments was conducted to identify the effects of key manufacturing process variable changes on the performance of flip chip underfill materials in a no-clean flux flip-chip assembly. The manufacturing process variables evaluated were: no-clean flux chemistry type; reflow profile; underfill dispense temperature.