IR Versus Hot Air Rework
When you investigate the various SMT/BGA rework stations available globally, you notice a number of manufacturers focusing on ‘mechanical superiority’ to mask a products poor thermal control.
Different mechanical features aimed at ‘improving’ the stations are continuously being developed and offered as ‘groundbreaking solutions’. But what about controlling the rest of the rework process? And how important are all these features? It’s relatively a simple process to align and place a BGA or CSP. In fact, many users we speak to manually manipulate the components with excellent results. That said, we have incredibly accurate, simple-to-use mechanical systems for alignment and placement for customers who want superior accuracy and assistance.
A superior rework station should have good mechanics but also have excellent thermal process control capability. You need to accurately align and place a component, then very, very accurately heat the PCB/component assembly through a reflow process to achieve decent soldered joints. Perfect temperature control of both the component and PCB are vital. If the system is not able to align/place, achieve and repeat accurate PCB/component temperatures, while also controlling the ramp-rates and dwell times, then it is not a good rework station.
Closely following a temperature profile is the safest way of reworking because the PCB, component, solder and flux are all designed to be heated within the parameters used in a reflow oven during manufacturing. Tight overall process control of the chemistry, mechanical and thermal accuracy will produce superior quality solder joints.
Although many hot air rework stations are able to learn the parameters during a desoldering profile, if you wanted to adjust a component's temperature at reflow by just a few degrees, you would have to alter gas temperature (and/or flow rates) to generate a secondary effect of altering the component temperature. Creating new profiles can be difficult and may often take hours to configure with some systems.
This is where Focused IR has a huge advantage over hot air rework as component temperatures can be instantly changed. Being tool-free with no nozzles and instantly controllable, it has enabled us to create true Auto Profiling software with real-time, closed-loop temperature control. PDR’s Focused IR has enabled us to make stations that are easy to set up and use. New profile set up times are now down to just a few minutes, a massive saving.
Today, our stations use software control, using inputs of component and PCB temperatures to completely and automatically control the thermal process. The software uses ‘real-time’ component and PCB temperatures to continuously adjust the Focused IR and automatically follow a thermal profile ‘target’.