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Decapsulation Technique for Copper Wirebonded Devices in Plastic Package

IP.com Disclosure Number: IPCOM000198399D
Publication Date: 2010-Aug-06
Document File: 2 page(s) / 206K

Publishing Venue

The IP.com Prior Art Database

Abstract

Copper wirebonded devices in plastic package are decapsulated using the mixture of fuming nitric acid and fuming sulfuric acid manually. This paper describes the effect of temperature and ratio of the acid mixture. The established acid decapsulation recipe is mixture of 1 part of 98% fuming nitric acid and 1 part of 20% fuming sulfuric acid at 90c. The Aluminum bond pad and Copper wirebonds are preserved with this acid decapsulation recipe.

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Decapsulation Technique for Copper Wirebonded Devices in Plastic Package

Abstract

Copper wirebonded devices in plastic package are decapsulated using the mixture of fuming nitric acid and fuming sulfuric acid manually. This paper describes the effect of temperature and ratio of the acid mixture. The established acid decapsulation recipe is mixture of 1 part of 98% fuming nitric acid and 1 part of 20% fuming sulfuric acid at 90°c. The Aluminum bond pad and Copper wirebonds are preserved with this acid decapsulation recipe.

Introduction

With the increasing price of Gold, the industry is seeking an alternative to replace the wirebonds with Copper for its better electrical and thermal conductivity as well as its relatively lower cost. However, the primary challenge comes when decapsulating the Copper wirebonded devices for failure analysis.

The conventional acid decapsulation method that uses fuming nitric acid to remove the mold compound cannot be used for Copper wirebonded devices as the Copper will react with nitric acid. Generally, in acid decapsulation, nitric acid and sulfuric acid is applied to etch the mold compound. In this paper, 98% fuming nitric acid and 20% fuming sulfuric acid are used to evaluate the effectiveness of decapsulating the Copper wirebonded devices. It is essential to fine tune the right proportion of these acids in order to preserve the Copper wirebonds, the Aluminum bond pads as well as its functionality.

In this paper, the devices are decapsulated using the manual acid decapsulation method, which mixed acid is dripped manually onto the mold compound on hotplate, rinse it with acetone and repeat the decapsulation process until the die and wirebonds are exposed. The manual acid decapsulation makes mass decapsulation possible in order to support wire pull and ball shear during Process Qualification and it is visual controllable.

Decapsulation Variables

I. Acid Temperature

The evaluation is carried out at proportion of 5 parts fuming nitric acid and 3 parts fuming sulfuric acid. The Aluminum bond pad corrosion increases when the temperature of mixed acid rises more than 90°C and eventually corroded completely when the temperature is above 130°C. However, the Copper wire diameter can be preserved at 25µm with the temperature above 90°C. Hence, it is deduced the effective temperature is at 90°C.

Fig 1. This graph shows the effect of acid temperature at 5:3 fuming nitric acid and fuming sulfur...