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Electronics Production | April 12, 2006

Using Focused Infra-Red To Simplify Lead-Free BGA Rework

The quality of BGA rework, so crucial to the profitability of any OEM or EMS provider and the single most important process in successful and profitable implementation of BGA technology, is down to mechanical accuracy, good materials and thermal control.
Not surprisingly, OEMs and EMS providers the world over spend a great deal of time developing thermal profiles for their rework that will guarantee the fastest, safest time to reflow. Creating a profile, however, can be frustrating, time-consuming and expensive.

But it doesn't have to be: some of the world's top OEMs and EMS providers rely on UK company PDR and its Focused Infra-Red (Focused IR) technology to simplify one of electronics manufacturing's riskiest, most demanding and unavoidable tasks.

Eliminating the risk and guesswork from thermal profiling, Focused IR uses Infra-Red light energy to take the board and component to a temperature that will not damage them, yet will melt the solder between them. Roger Gibbs, pioneer of Focused IR technology and co-founder and
Managing Director of PDR, explains how it works: "We call it passive heat, Focused IR heats the object directly, rather than heating the air around it, so even though there is enough energy to get a component to the right temperature, you can safely put your hand in the beam, even at full power".

For topside heating, PDR uses a 150W IR lamp whose short and medium length IR emissions are refocused by PDR's lens system into a visible spot whose diameter can be adjusted manually to cover the component to be reworked. This is facilitated by the distance of the lens system from
the board, which enhances visibility and access.

The real secret to effective reflow, is in pre-heating the board, so PDR's BGA rework systems use a powerful 1600W medium-wave IR panel back heater that ensures even more control over how much energy is put into an assembly.

Control is essential to successful rework, especially when reflowing at the higher temperatures required by lead-free solders, and PDR's non-contact IR heat sensor is key, monitoring precisely the temperatures of the board and component in real-time. "As these temperatures are directly related to solderball temperature, we know exactly when reflow occurs", explains Gibbs.

The real revolution, though, lies in combining the heat sensor with PDR's simple-to-use profiling software: with no need for tests or prior profiling work, the system automatically ensures that even a board and component that are completely new to it will ramp at the right rate to the right temperature and soak for the right time for their size and application, following a solder manufacturer's or PDR's own default profiles. The system controls how much energy is required 4 times a second and keeps temperature at all times to within 2°C of target profile.

Where soak times have to be altered, PDR's software and the real-time temperature feedback ensure accuracy while simplifying the operation.Gibbs: "It's so simple it takes longer to work out how to align and place the component than it does to set up a thermal profile. Focused IR is ideal for professional BGA rework, large components need quite a lot of energy, which, for hot gas systems, means a higher gas flow. This can be a problem as BGAs are typically surrounded by small chips and resistors that can be blown away - a problem that increases when you get to higher temperature lead-free processes".

Accessibility on densely packed boards is an additional problem for hot gas systems, which call for a range of nozzle geometries for different component types. With PDR's systems, the operator simply positions the heat energy spot and adjusts its size to the component to be reworked -
no access problems and no nozzle changes. The main advantage of Focused IR, though, is that the temperature of replaced components can be measured in real-time using the non-contact heat sensor - something that is impossible with hot gas systems, yet which is essential when using
the potentially damaging higher temperatures needed for lead-free solders, as Gibbs observes: "As it is gas that heats up the board and the component, the gas temperature must be beyond the target
temperatures, creating a risk of heat damage. Some of the better systems avoid these problems with more effective back heating and better temperature control, but there are many more systems that could create damage".

Once you've got your thermal profiling under control, Gibbs believes you are 40% of the way to good rework quality. Materials take you a further 40%, and the remaining 20% is down to good alignment and placement systems. Here too, PDR has a solution: its top BGA systems come with
easy to use split-beam prism alignment and placement features that guarantee damage-free component handling.

With its Focused IR technology, non-contact heat sensor and profiling software, PDR has revolutionised rework, eliminating the guesswork and replacing it with real-time profiling for rework professionals, who are already using PDR's systems in their lead-free BGA processes around the
world.

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