TECHNICAL ADVANCE IMPROVES REFLOW PROCESS RELIABILITY AND CONSISTENCY
Author: Brad Bailey Company: Electrovert USA Corporation Date Published: 4/28/1997
Surface Mount International
Abstract: Trends in electronics assembly continually increase production numbers. Reliability- and maintainability of equipment in the production line is implicit in the concept of increasing throughput and profit margins. Capital cost of equipment is frequently less the half of the total life cycle cost. As a result maximum cost effectiveness is achieved only when equipment is designed with tenants of reliability and maintainability in mind. Cooling module performance is the primary weakness of many inert reflow oven designs, Most designs use a combination blower and heat exchanger to intake process gas, pass it through the heat exchanger, then direct the cool gas onto the product. Combination of high volume throughput and re-circulated atmosphere for nitrogen savings results in fouling of heat exchangers by flux components in the process gas. This effect is exacerbated by enhanced printability pastes which often leave viscous residues. Fouling of these systems over time leads to steady and uncontrolled loss of cooling performance. Lack of reflow process consistency and control results. Preventative maintenance is required when cooling performance reaches some minimal level. This causes frequent downtime; typically once per two to six week period for high volume production. Reliability and maintainability must be increased for better performance. A novel laminar gas stream cooling system addresses these problems. This system provides consistent cooling through out a greatly extended maintenance interval. This cooling technique was developed from failure modes and effects analysis (FMEA) of typical blower/heat exchanger cooling systems. This cooling technique utilizes physical sound principles based on mass flow and heat exchange to offset flux fouling of the cooling module. Keywords: reflow cooling, maintenance interval, cooling rate, microstructure, cost/benefit analysis.