Dense-Pitch Copper Wire Bonding for Double IC Chip Stacks
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge in bonding dense-pitch small-pad IC chip packages with pitches less than 43 μm is controlling the diameter of the bonding ball to prevent short circuits and damage to adjacent wires, due to the tight spacing and difficulty in maintaining the required wire diameter and clearance during the bonding process.
Innovation Solution
A dense-pitch small-pad copper wire bonded double IC chip stack package is developed, featuring a lead frame carrier with IC chips stacked and pads arranged in parallel lines, where metal balls are implanted and connected with copper bonding wires, ensuring precise control over bonding ball diameters and spacing to avoid short circuits and wire damage, using a multiple-ball welding method that forms copper bonding wires by looping and arching between chips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a phi 15 μm or phi 16 μm copper wire is used for bonding, then the wire diameter increases which should improve bonding strength, but the bonding ball diameter becomes difficult to control and may exceed the pad size causing short circuits
Solution Approach 1:
The patent changes the bonding parameters by using a phi 15 μm copper wire with specifically controlled bonding conditions to form balls with diameters of 35-38 μm, which are precisely controlled to prevent short circuits while maintaining adequate bonding strength for dense-pitch applications
Solution Approach 2:
The patent performs preliminary actions by carefully controlling the wire diameter selection and bonding process parameters before actual bonding occurs, ensuring that the bonding ball diameter is pre-determined to be within the safe range (35-38 μm) that prevents short circuits between adjacent pads
2Productivity
If the wire spacing is reduced to accommodate dense-pitch pads, then more pads can be bonded, but adjacent welding wires may be damaged by hit during the bonding process
Solution Approach 1:
The patent applies local quality by creating different structural characteristics at different locations: the bonded wire structure has adequate spacing and arching at critical locations to prevent damage, while maintaining high bonding density in the overall layout, allowing each local area to have optimized properties for its specific function
Solution Approach 2:
The patent transitions from a two-dimensional planar bonding approach to a three-dimensional structure by forming arched bonding wires that loop between chips, adding the vertical dimension to accommodate dense horizontal spacing while maintaining wire integrity through the arching configuration
3Productivity
If the pad size is reduced to increase chip density, then more chips can be packaged, but the clearance between adjacent pads decreases making bonding more difficult
Solution Approach 1:
The patent uses the vertical dimension by forming arched bonding wires that loop between stacked chips, allowing bonds to be made through the third dimension rather than relying solely on horizontal clearance, thereby enabling dense-pitch bonding with reduced pad sizes while maintaining manufacturing feasibility
Solution Approach 2:
The patent segments the bonding process into multiple stages with distinct functions: first bonding wires are formed with specific ball diameters, then additional wires are bonded with different configurations, allowing each bonding operation to be optimized independently for the reduced pad pitch conditions
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively prevents short circuits and wire damage, enabling reliable multi-chip stack and packaging while improving bonding intensity and reducing wire costs, with enhanced product quality and economic benefits.
Implementation Method 1
In a normal ball welding binding process, the qualified diameter of a welded ball is larger than/equal to 2 times of a wire diameter
Data Source
AI summary
A dense-pitch small-pad copper wire bonded double IC chip stack package comprises a plastic package body, in which a lead frame carrier and a frame lead inner pin are arranged; the upper surface of the lead frame carrier is fixedly connected with a first IC chip; a second IC chip is stacked on the first IC chip; the upper surface of the first IC chip and the upper surface of the second IC chip are respectively provided with a plurality of pads which are arranged as two lines of pad groups in parallel; the two pad groups are respectively a first pad group and a second pad group; a metal ball is implanted on each pad; each metal ball is connected with a first copper bonding ball; and a third copper bonding wire is formed by looping and arching on a corresponding metal ball between the second IC chip and the first IC chip. The preparation process of the present invention comprises thinning, scribing, loading the chip, performing pressure welding, plastic packaging and post-curing, trimming, electroplating, printing, forming and separating, and packaging. The package and the preparation method of the invention avoid the hidden danger of open circuit of a plastic packaging punching wire caused by the crater on the pad, the short circuit of adjacent welding spots, and the easy damage of a previous wire.