Three-Dimensional Paddle Shift Modeling for IC Packaging

[+] Author and Article Information
Chien-Chang Pei

Department of Mechanical Engineering,  National Cheng Kung University, Tainan, Taiwan

Sheng-Jye Hwang

Department of Mechanical Engineering,  National Cheng Kung University, Tainan, Taiwanjimppl@mail.ncku.edu.tw

J. Electron. Packag 127(3), 324-334 (Dec 02, 2004) (11 pages) doi:10.1115/1.1938986 History: Received April 19, 2004; Revised December 02, 2004

The plastic packaging process for integrated circuits is subject to several fabrication defects. For packages containing leadframes, three major defects may occur in the molding process alone, namely, incomplete filling and void formation, wire sweep, and paddle shift. Paddle shift is the deflection of the leadframe pad and die. Excessive paddle shift reduces the encapsulation protection for the components and may result in failures due to excessive wire sweep. Computer-aided analysis is one of the tools that could be used to simulate and predict the occurrence of such molding-process-induced defects, even prior to the commencement of mass production of a component. This paper presents a methodology for computational modeling and prediction of paddle shift during the molding process. The methodology is based on modeling the flow of the polymer melt around the leadframe and paddle during the filling process, and extracting the pressure loading induced by the flow on the paddle. The pressure loading at different times during the filling process is then supplied to a three-dimensional, static, structural analysis module to determine the corresponding paddle deflections at those times. The paper outlines the procedures used to define the relevant geometries and to generate the meshes in the “fluid” and “structural” subdomains, and to ensure the compatibility of these meshes for the transfer of pressure loadings. Results are shown for a full paddle shift simulation. The effect on the overall model performance of different element types for the mold-filling analysis and the structural analysis is also investigated and discussed. In order to obtain more accurate results and in a shorter computational time for the combined (fluid and structural) paddle shift analysis, it was found that higher-order elements, such as hexahedra or prisms, are more suitable than tetrahedra.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Paddle geometry and constraint boundary conditions

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Figure 2

Paddle deflection caused by nonuniform loading induced by EMC flow

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Figure 3

Flowchart of the paddle shift analysis methodology

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Figure 4

Extruding triangle and quadrilateral elements to prisms and hexahedrons

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Figure 5

Left: the solid model of a TSOP; Right: the cross section

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Figure 6

Sliced layer structure of TSOP package

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Figure 7

Package layer information

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Figure 8

Schematic illustration of the meaning of the “compound surrounded” parameter

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Figure 9

Schematic illustration of the “divide” parameter

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Figure 10

2D outline definitions by rectangles

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Figure 11

2D drawing, including the leadframe, die, and package outlines

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Figure 12

Gathering a closed-line loop to define a “region”

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Figure 13

Leadframe outline defined by many regions. The word in each bracket is the name of the region

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Figure 14

Finished solid model

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Figure 15

2D mesh inside the package outline

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Figure 16

Rule for element extrusion: (a) original 2D element and (bd) generated elements using different rules

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Figure 17

Guideline for element extrusion for the mold-filling analysis

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Figure 18

Fluid-flow mesh used for mold-filling analysis

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Figure 19

Stair-stepped approximation for inclined parts (such as the downset)

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Figure 20

Predicted melt front of the EMC during the molding process

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Figure 21

Flowchart of the paddle loading distribution analysis

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Figure 22

Total leadframe outline (left) versus paddle outline (right)

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Figure 23

Rule for element extrusion for the paddle mesh generation

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Figure 24

Illustration of downset elements generation and the paddle mesh used for structural analysis

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Figure 25

Registration of elements on the common boundary between the fluid-flow mesh and the paddle mesh (only some representative elements are shown)

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Figure 26

Element registrations of two meshes: (a) paddle mesh, including its coordinate system; (b) fluid-flow mesh, including its coordinate system; (c) the two meshes combined by aligning their coordinate systems. (d) Element faces have the same coordinates in an element pair.

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Figure 27

Illustration of the mismatch of the downset element boundaries between the fluid-flow mesh and paddle mesh

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Figure 28

Data transfer from the fluid-flow mesh to the paddle mesh according to the preestablished element relation

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Figure 29

Pressure loading on the paddle mesh at different filling times

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Figure 30

Boundary conditions with fixed nodes at the end of paddle: schematic diagram (left) and boundary conditions specified for the simulation (right).

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Figure 31

Paddle deflections in the z direction at different filling times. From top to bottom, the filling times are 1, 2, 3, 4, 5, and 6s, respectively. The thin lines represent the original paddle profile, and the thick lines represent the deformed profile with a scale factor of 60 in the z direction.

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Figure 32

(a) Original mesh, (b) refined mesh obtained by increasing the 2D element count, (c) refined mesh obtained by increasing the number of layers

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Figure 33

Illustration of the parameter to be used for comparison of the deflection results obtained with different meshes

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Figure 34

Deflections versus number of paddle elements

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Figure 35

Deflections versus number of paddle nodes

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Figure 36

Computation time versus element count of the fluid-flow mesh




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