Efficient Escape Routing Rui Shi, Chung-Kuan Cheng University of California, San Diego
Our Research Works Escape routing bottleneck analysis Efficient escape routing for square array central triangular method two sided method sierra method Efficient escape routing for hexagonal array
Problem Definition Problem: Escape the I/Os in an area array to the outside. Area Array: Full populated array: all I/Os are taken into consideration for analysis Escape Routing: Assume blind vias are used Objective: Maintain high density of I/Os in array Reduce the number of routing layers used for escaping Applications: Interconnection from chip to package Interconnection from package to board
Escape routing bottleneck analysis Maximum flow formulation Build routing graph for the area array Solve maximum flow problem on the routing graph Define bottleneck edge as the edge whose flow is equal to its capacity Define bottleneck contour as the profile formed by all the bottleneck edges The maximum flow solution is a upper bound
Escape routing bottleneck analysis (Cont.) Escape bottleneck experimental results Parameters used: the pad pitch = 150 m the pad diameter = 75 m the line width = 20 m the spacing = 20 m the array size = 40 Six square area array patterns
Escape routing bottleneck analysis (Cont.) Maximum flow value = Maximum flow value =
Escape routing bottleneck analysis (Cont.) Maximum flow value = Maximum flow value =
Escape routing bottleneck analysis (Cont.) Maximum flow value = Maximum flow value =
Escape routing bottleneck analysis (Cont.) Conclusions: The bottleneck contour always follows the outline of the array The array outline with larger capacity has the potential to decrease the number of routing layers I/Os escaped in previous layers will form the outline for the following layers
Efficient escape routing for square array Central triangular method Escape I/Os from the center of the outside row and expands the indent with a single triangular outline. In this method, the outline capacity is increased continuously layer by layer.
Efficient escape routing for square array Two sided method Escape I/Os from inside and outside simultaneously. The outline will shrink slowly and follow zigzag shape.
Efficient escape routing for square array Sierra method Escape I/Os from the center of the outside row and expands the indent with a sierra triangular outline. Break out I/Os in every layer as many as possible.
Experimental Results LayerRow by rowParallel triangularCentral triangularTwo sided x 40
Experimental Results LayerRow by rowParallel triangularCentral triangularTwo sided x 20
Efficient escape routing for hexagonal array Using same area and same I/O pitch, the hexagonal array can hole more I/Os and have larger I/Os density Using same area and holding similar number of I/Os, the hexagonal array can separate the I/Os loosely and have larger I/O pitch
Efficient escape routing for hexagonal array Size nSquare grid arrayHexagonal arrayIncrease # rows# I/Os# rows# I/Os % % % % % % %
Efficient escape routing for hexagonal array Column-by-Column Horizontal Escape Routing
Efficient escape routing for hexagonal array As long as the condition is satisfied, I/Os in the hexagonal array can be escaped within the same number of routing layers as square grid array Flip ChipFBGA/CSP Year Pitch Pad Diameter Line Width Line Spacing Condition unit: m (ITRS)
Efficient escape routing for hexagonal array Two-sided Horizontal/Vertical Escape Routing
Efficient escape routing for hexagonal array Multi-direction Hybrid Channel Escape Routing
References M. Horiuchi, etc., “Escape routing design to reduce the number of layers in area array packaging”, Advanced Packaging, IEEE Trans., 2000 A. Titus, etc., “Innovative Circuit Board Level Routing Designs for BGA Packages”, Advanced Packaging, IEEE Trans., 2004 R. Shi, etc., “Layer Count Reduction for Area Array Escape Routing”, IMAPS International Conference and Exhibition on Device Packaging, 2005 R. Shi, etc., “Efficient Escape Routing for Hexagonal Array of High Density I/Os”, DAC, 2006 R. Wang, etc., “Layer Minimization of Escape Routing in Area Array Packaging”, ICCAD, 2006