Chahn Lee

Phenomenological Hysteresis Modeling Based on Asymmetric Transition Probability of Magnetization

An accurate and efficient static hysteresis model is proposed that phenomenologically describes hysteretic properties based on the asymmetric transition probability of magnetization. The transition probability function is determined from first-order reversal curves. The model provides magnetic hysteresis curves using a simple function calculation without any assembly of hysterons. A comparison with measured properties of silicon steel shows that this model represents hysteretic properties, including minor loops more accurately than the play-hysteron-based model.

Development of Sn-Pb-Bi solder materials for fine pitch package

This paper describes a new solder which is less likely to result in solder bridging. In this research, it was clarified that the bridging was related with surface tension and temperature difference of solidus and liquidus at a solder composition. We have selected 53Sn-2Bi-45Pb solder from results of experiment. Bridging occurrence rate of this solder is less than 1/10 of 63Sn-37Pb solder in cases of 0.5 mm and 0.3 mm pitch QFPs soldering.

The analysis on bridge between leads of quad flat package in reflow soldering on printed circuit boards

The factors occurring bridge between leads of Quad Flat Package (QFP) have been studied based on potential theory. To find out the analytical property of bridge configuration between leads, it is assumed that the configuration of bridge is approximated by a solid of rotation, which the rotating curve is given as r+ax/sup 2/. The physical property of the bridge can be a good approximation compared with the bridge that is constructed by Laplace formula, and can describe the potential of occurrence of bridge accurately. The occurrence of bridge is one of bifurcation phenomena. Then, there is a branch point to decide to whether bridge occurs or not. It is proved that this branch point, represented as a saddle point of energy surface, is function of geometrical elements, such as width of lead and pad, and gap between pad and lead, etc., together with surface and adhesion tension of solder. It is also found that the most dominant factor of occurrence is the gap between lead and pad. There is the optimum width of pad and lead, which is the minimal condition of bridge occurring, independent of surface and adhesion tension of solder at given pitch of leads of QFP.

New estimation method of wetting and surface tension by measuring area of spreading solder in flux atmosphere based on ellipse approximation of Sessile drop configurations

A method for analyzing the wetting behavior which allows estimation of the movement path and final form of molten solder has been developed. This method is based on an energy analysis which considers the total balance, as opposed to the local balance contact angle method used conventionally for analyzing wetting behavior. In this report, the method is applied to the spreading of solder balls, and the effects of physical properties on wetting behavior are examined. It is found that the physical property which influences the wetting behavior the most is the ratio of wetting tension to surface tension, and this ratio is suitable as a parameter for analyzing soldering defects such as solder bridges.