We offer “Evaluation and Analysis of Semiconductor Package”

Hello, everyone. I’m Goto from the package design section of the Tokyo office.

I am mainly responsible for the evaluation and analysis of semiconductor packages (also known as IC packages and LSI packages).

In this blog, I will explain a comparison between gold and copper wires used in semiconductor packages and related evaluation and analysis.

Wires are used to electrically connect IC chips and external terminals (lead frames and solder balls) inside semiconductor packages. Figure 1 and Figure 2 show the structure of the major semiconductor package types.

 

 

I’ll explain a comparison between gold wire, and low-priced copper wire increasingly used in recent years due to the soaring price of precious metals, using the semiconductor packages shown in Fig. 1 and Fig. 2.

The general merits and demerits of copper wire are as follows. Although copper wire offers significant material cost advantages over gold wire, it has some disadvantages.

< Merits >

  • Low material costs
  • High thermal conductivity
  • High electrical conductivity
  • High elastic modulus that makes the wire less likely to be deformed at injecting of resin
  • Superior high temperature tolerance due to the slow growth of intermetallic compounds with the aluminum pad of the IC chip

< Demerits >

  • Easy to oxidize which can affect the joint strength
  • High ionization tendency and easy to corrode
  • Pad cracks are likely to occur during wire bonding to IC chip due to the hardness of the material

General wire evaluation and analysis items are shown in Table 1. The evaluation and analysis of a semiconductor package using copper wire first focuses on the aforementioned issues. In an evaluation and analysis of semiconductor packages using copper wire, it is necessary to pay attention to the corrosion of the wire since a resin solvent is used for the resin opening process, and to proceed it quickly to eliminate the effects of oxidation after opening the package.

 

Table 1. Items for evaluation and analysis of wires

Items

Objects ( Checking points )

Observation of bonding between wire and aluminum pad of IC chip

  • Wire bonding assembly conditions
  • Joint surface
  • Effects of corrosion and oxidation

Observation of the shape of the junction between a wire and an IC chip, lead frame, and a substrate

  • Wire bonding assembly conditions
  • Cross-sectional shape of the joint
  • Pad cracks caused by wire bonding

Bonding strength measurement between wire and IC chip aluminum pad

  • Wire joint strength
  • Effect of corrosion on material strength

Observation of wire loop shape

  • Wire bonding assembly conditions
  • Wire deformation during molding and sealing

 

If one wire has a problem, it will affect the quality of the product, so it is necessary to check it. Semiconductor packages are made up of various materials, and we also evaluate and analyze the bonding status and appearance of each combination of other materials.

We will continue to introduce a variety of semiconductor package related topics in the future.

 

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