As the cost per printed circuit board (PCB) increases, it is becoming more important to reduce both the scrap rate and returns caused by improper rework. Although modern production equipment and processes have been working toward the goal of a 100% first pass yield, this still remains unachievable. The smaller process windows and higher process temperatures required for a lead-free process have further complicated the matter. It is precisely for this reason that major OEMs and contract manufacturers are spending additional energy in the thorough evaluation of a safe and efficient lead-free rework process.

One of the BGA rework systems the EMPF utilizes is the Ersa IR/PL 650 (Figure 5-1). This third-generation IR rework system offers three new technological innovations: DynamicIR, Multi True Closed Loop Control, and IntelligentIRS.

The DynamicIR principle for selective reflow
Precise temperature control on the board and component is the ultimate goal in rework. The safe medium wavelength IR heating technology allows for uniform heat distribution from the top and bottom side across the PCB and component. The DynamicIR technology allows for the fully automatic dynamic control of the top (1400W / 60mm x 120mm) and bottom (3200W / 350mm x 450mm) IR heaters depending on the actual temperature of the component and where it is in the temperature profile. The total available power (4600W) to the selective reflow system is spread across 4 separately switchable heating zones on the top and 5 zones on the bottom. Depending on board size, the thermal mass of the substrate, and component size, the DynamicIR technology will deliver the required heat energy at the precise time and location in order to ensure that the component and board exactly follow the prescribed temperature profile. Combined with the enhanced capability to run an extended or flat peak, this technology affords the lowest temperature deltas across the component, and greatly reduces PCB warpage.

The Multi True Closed Loop Control principle
Temperature control on the board and component is a critical to any BGA rework system. True Closed Loop Control means that the actual component temperature is acquired, using a patented IRS non-contact Infrared sensor and is used as the primary control mechanism for the heating system. The new IntelligentIRS allows for a more precise temperature measurement by choosing from a component table or by component-specific IRS calibration. Either the IRS or a K-type NiCrNi TC sensor of choice can be chosen to drive the DynamicIR heating technology, thus providing a perfect profile every time.

Multi True Closed Loop Control builds on and enhances this principle by using up to 4 additional TC sensors. By assigning threshold values to these additional sensors, they are used to prevent the fully automatic DynamicIR heating system from undesired overheating of adjacent or bottom side components. The heating system automatically reduces or increases energy respectively to the top and bottom IR heaters in order to provide a set of threshold temperature is not exceeded. A First Pass Yield for rework is thereby provided.

The “Lead Free Safe Heat” result
True temperature control on the board and component is the key to a safe lead free rework process. The higher working temperature and the smaller process windowsl makes the lead free rework process a much greater challenge. The risk of overheating adjacent or bottom side components during rework is greatly increased. The DynamicIR and Multi True Closed Loop Control principles afford the highest level of rework safety by literally making it impossible to overheat beyond an assigned threshold value, thereby making it impossible to work outside a specified lead free process window.

The complete system is broken down into four modules: the IR650 selective-reflow module (as described above), the RPC reflow-process camera module, the PL650 precision-placement module, and the IRSoft software module. The RPC module uses a high-power (up to 300x enlargement) motor-zoom camera, a controllable LED ring lighting system and an extremely robust, movable stand. The reflow process can be visualized from multiple angles on even the smallest of components.

The IRSoft is the control and documentation software for the IR/PL 650. This user-friendly software provides both the interface simplicity required for less skilled operators, as well as the advanced profiling and documentation requirements of a highly trained user. This database-incorporated software offers a high level of flexibility and operator customization capability. If you want to see a demonstration of this system, please contact Robert Berta at the EMPF, 610-362-1200 Ext 253 or rberta@aciusa.org.