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# Pad Placement Algorithm for four-sided packages

IP.com Disclosure Number: IPCOM000017502D
Original Publication Date: 2001-Jan-01
Included in the Prior Art Database: 2003-Jul-23
Document File: 9 page(s) / 721K

Siemens

## Related People

Ho Chew Choy Paul: AUTHOR

## Abstract

The idea of this invention is the development of an algorithm that can quickly perform pad placement for a given IC using T/MQFP packages. The algorithm can be effectively used in a CAD tool for package feasibility analysis performing the very early stage of pad placement for the floorplanning tool. By doing so, it is able to judge in a very early stage of the design if a design can use a particular package and evaluate the costs involved. 1. Conditions for successful placement

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 39% of the total text.

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Information / Kommunikation

Pad Placement Algorithm for four-sided packages

Idee: Ho Chew Choy Paul, Singapore

The idea of this invention is the development of an algorithm that can quickly perform padplacement for a given IC using T/MQFP packages. The algorithm can be effectively used in aCAD tool for package feasibility analysis performing the very early stage of pad placement for thefloorplanning tool. By doing so, it is able to judge in a very early stage of the design if a design canuse a particular package and evaluate the costs involved.

1. Conditions for successful placement

The initial condition for complete successful placement of digital pads along the peripheral of achip must meet equation (1):

å

Nn

Wp

+

å

n

4� Wc

n

£

2

x

(

W

+

H

)

(1)

=

1

n

=

1

Where,

Wp = width of digital pad cell

Wc = width of corner pad cell

W = width of chip

H = height of chip

Fulfilling equation (1) might not guarantee a full placement of pads, this is because pads cannot beplaced over corner pads, and the order of the placement of the pads will have also an impact tothe actual requirement for chip size.

The condition for successful placement of the chip is for any side of the chip:

k

side

kn

N

L

xWc

Wp

=

£

+

(2)

å� � 2

/

n

=

1

Side

=

K

Siemens Technik Report

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i.e. the sum of pads placed on that particular side must be able to fit into the length of thatparticular side.

These two conditions set the basis for the placement. Now, the discussion of the algorithm forinitial placement of pads on a particular side of the chip follows.

In order to derive an initial placement of pads on a chip side, the first thing to do, is to derive anoptimum mounting condition for the pad. A suggestion is that the pads should be placed on a linewith die centre point and bonding finger. Figure 1 illustrates this suggestion using the upper leftfour fingers of the leadframe:

Figure 1: Optimum mounting condition

Siemens Technik Report

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Figure 2: Blown up of upper left corner of chip edge centre line projection

From Figure 2, the intersection of the projection line and the chip edge will form a boundary atwhich the pad should be placed. The second projection point is given by the intersection of thebottom boundary of the corner cell projection line and the projection line from centre of chip tothe finger opening as shown in Figure 3 below.

Figure 3: Obtaining the second boundary placement point for a pad

A set of two points can be obtained for any connection to a pin of the leadframe. These twopoints are obtained from the intersection of the chip edge with the centre projected line (e.g. L1 inFigure 3) and the intersection from the projected bottom edge of the corner cell with the centreprojected line.

Siemens Technik Report

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Hence, for any connection of pad to pin of a leadframe, a set of points...