09 Jun

Repeatable method - Decapsulation of silver alloy wiring packages

Posted by Florie

 

Decapsulation of packaged devices is devoted to exposing the internal components of the package. It is a key technique for all reliability investigations of products. Functional decapsulation is used on many services performed by SERMA such as failure analyses, chip modifications, qualifications (radiation hardening, pull-shear test) and characterizations (electrical, construction analysis, …). The challenge in functional opening of a device is to keep physical and electrical integrities of the semiconductor die. Among this process, wire bonding is the main sensitive element.

At its origin, bonding wires were made of gold (Au). However, in the last few years, a huge increase in the price of Au has driven to the need for lower cost wire materials. Copper (Cu), Palladium Coated Copper (PCC) alloy wires have emerged as alternatives to Au bond wires. Cu-based wires are low cost and have excellent electrical resistivity. However the hardness of copper makes it difficult to use in many applications such as those with fragile bond pad structures. Recently, a new type of bonding has been introduced: Silver (Ag) wire.

 

 

This new type of wire offers physical properties similar to those of gold while its cost is similar to that of copper.

 

The introduction of a new type of bonding wire has obliged laboratories to adapt the methods used for decapsulation. As it has been done for Copper wires, Serma Technologies recently introduced a new and reproducible method of decapsualtion. This method is based on a new chemical recipe. The dedicated Ag chemical recipe used is based on add on of Iodine into usual acid mixture used for Au and Copper wire bonds based package:

8 . HNO3 + 6 . Ag => 6 . AgNO3 + 2 . NO + 4 H2O

KI (aq) + AgNO3(aq)  => AgI + KNO3(aq)                                 [1]

[1] ISTFA 2015 : M. Lefevre, E. Noraz, D. Veychard : Repeatable method for automated decapsulation of silver alloy wire packages

First trials made on device using Ag wires have clearly shown that conventional techniques cannot be applied to this process. By using it, wires are completely destroyed by chemical recipes as shown below.

Opening of Ag wires with conventional acid recipes: 

Dedicated flow for functional opening of Ag wiring:

 

Validation of new opening process

 

SERMA Technologies demonstrated the efficiency of the newly introduced process.
Both the physical integrity and mechanical robustness investigations highlighted that functional opening of Ag bonding wire system was under complete control into the laboratories.

Both the physical integrity and mechanical robustness investigations highlighted that functional opening of Ag bonding wire system was under complete control into the laboratories (Grenoble/Pessac).

Coupled to a laser decapsulation system, SERMA Technologies is able to complete the most challenging and advanced functional openings by considering any type of bonding wire (Au, Al, Cu and Ag).