Method for diagnosing the life of a solder connection

A method performed in a computer, for diagnosing a connection life of a solder connection between a substrate and parts loaded thereon, said computer including input means for inputting information, processing means for processing said input information and outputting a result of said processing and display means for displaying said results of said processing, said method comprising the steps, performed by said computer, of:

• inputting by said input means parameters of a plurality of different solder connections of the same connection structure;
• calculating by said processing means shearing strains of said plurality of different solder connections;
• calculating by said processing means equivalent strain amplitude corresponding to thermal fatigue lifetime for each of the values of said plurality of shearing strains;
• defining by said processing means a relationship between said shearing strains and said equivalent strain amplitudes;
• formulating by said processing means a life evaluation criterion equation expressed using said equivalent strain amplitude;
• inputting by said input means a total crack length and a particular crack advancement by the very last cycle of a number of heat cycles applied to said plurality of different solder connections;
• determining by said processing means a crack length/crack advancement speed correlation model thereby obtaining solder connection life diagnosing model with said equivalent strain amplitude;
• inputting a desired parameter of said solder connection to be diagnosed of said same connection structure;
• determining by said processing means a corresponding equivalent strain amplitude corresponding to said desired parameter by using a relationship between said shearing strain and said equivalent strain amplitudes,
• substituting said equivalent strain amplitudes for the life evaluation criterion equation to acquire the connection life of said desired parameter;
• and
• displaying by said display means the life of said connection;
• wherein an equation for diagnosing the advancement of a crack is made using said equivalent strain amplitudes, and said equivalent strain amplitude is substituted for a crack advancement diagnosing equation to calculate the length of the crack;
• wherein said inputting step includes the steps of defining a member for which the life of the solder connection is to be diagnosed to display on said display means a shape model of the member,
• inputting by said input means required parameters representative of the shape of the connection in accordance with the shape model displayed on said display means,
• inputting required material constants for the member to be evaluated, and
• inputting an analysis condition of the member to be evaluated;
• said method further includes the step, performed by a computer, of
• performing by said processing means a calculation in accordance with said solder connection life diagnosing model and said crack advancement diagnosing equation;
• and
• wherein said displaying step includes the step of
• displaying the calculation result as a length of the crack on the shape model on the display means, and illustrating said diagnosing result on a solder connection life diagnosing graph representative of the relationship between the number of temperature cycles and the length of the crack.