Task Scheduling Control of BGA Solder Joint Process in Flexible Manufacturing System Abstract – This paper describes an open loop control method of the solder joint process in a rework station for faulty Printed Circuit Board (PCBs) containing electronic components in packages Ball Grid Arrays (BGAs). In particular, a mathematical model describing the solder joint process is, first of all, obtained. Then, the desired thermal profile of the junctions BGA-PCB is determined according to the physical constraints of the rework station framework. The control parameters corresponding to the above desired thermal profile are identified using the above mathematical model. Finally, the open loop control algorithm is implemented on the supervisor interface of the rework station in order to carried out experimental validation of the proposed method. 1. Introduction In the flexible manufacturing system (FMS) of electronic devices, the increasing request of integration of more and more functions in a single die, in order to obtain small components with low working currents, has as a result the gradual disuses of Pin Through Hole (PTH) insertion technology of the electronic components to advantage of Surface Mounted Technology (SMT) [1]. As is well know, the SMT technology is divided in two subfamilies. The first consists of components whose terminations fall in the boundary of the packages and is known as Fine Pitch Technology (FPT) and Ultra Fine Pitch Technology (UFPT). It is characterized by a lead pitch upper to 450 micron and a high pin count. The second is called Area Array (AA) and consists of BGA (Ball Grid Array) packages [2]. The principal characteristic of the BGA package [3] is the connection placed on the bottom side of the component exploiting the whole area under it. In this way it is possible to increase the number of I/O terminations (actually upper 5000), without reduction of the lead pitch. This allows to increase the upper cut-off frequency of the component due to the reduction of the parasite capacities and inductances. However, the BGA packages present inspection and assembly problems specially in the rework process [2], [4]. Actually the closed loop control of the thermal profile of the welding process of the component on the PCB is not reproducible, as in the reflow oven, because the balls are not directly accessible for measurement. In order to give the correct quantity of heat to all the welding joints, dedicated rework stations are used which simulate the thermal environment inside the reflow oven in the principal production chain [2]. The control parameters used to plan the task scheduling actions of the rework station are obtained off line during the setup operation, and then stored in the supervisor interface to be used during the rework cycle. These parameters can be obtained either by trial and errors or direct methods. In the trials and errors methods, the parameters are identified after a lot of test cycles executed on the PCB. Starting from a set of acceptable initial values, the control parameters are adjusted according to some empiric rules so as to reduce the mismatch of the actual thermal profile corresponding to the actual values of the parameters themselves and the desired thermal profile. This method requires a very long F.Alonge Dipartimento di Ingegneria dell’Automazione e dei Sistemi University of Palermo Viale delle Scienze 90128 Palermo, Italy alonge@unipa.it F. D’Ippolito Dipartimento di Ingegneria dell’Automazione e dei Sistemi University of Palermo Viale delle Scienze 90128 Palermo, Italy filippo@unipa.it F.M. Raimondi Dipartimento di Ingegneria dell’Automazione e dei Sistemi University of Palermo Viale delle Scienze 90128 Palermo, Italy raimondi@unipa.it V.Aiello Dipartimento di Ingegneria dell’Automazione e dei Sistemi University of Palermo Viale delle Scienze 90128 Palermo, Italy aiello@ias.unipa.it 0-7803-9402-X/05/$20.00 © 2005 IEEE