Removing epoxy underfill between neighbouring components using acid for component chip-off

In addition to traditional high temperature eutectic soldering, the use of underfill epoxy to glue the electronic components to the PCB (memory, CPU, cryptographic chips) has now become the norm among mobile phone manufacturers, e.g. Apple, BlackBerry and Samsung. Currently, this technique is the best solution to protect components against various mechanical stresses and improve reliability. Unfortunately, traditional techniques (chip-off or lapping) have become impossible to apply to underfilled components without destroying them or without moving peripheral electronic components. These component movements make the board unusable or require many hours of expensive repairs and specific hardware. Acids and their use can be of interest in the digital forensics domain. Firstly, they can be used to de-capsulate the packaging of the electronic components before reading the chip (physical dump by chip-on), or to carry out reverse engineering of secure systems by micro-reading techniques of the silicon chip. Moreover, as we show in this paper, with the arrival of the latest generations of mobile phones, acid mixtures can be of interest if investigators want to use classical chip-off method (or the legal transplantation of damaged phones) for phones using underfill epoxy which cover the neighbouring components together (CPU, memory, capacitors, etc.). This work introduces a new method called “underfill acid corrosion”. The proposed process is based on the use of different mixtures of acids heated to various temperatures. We quantitatively study the influencing factors on the efficiency of acid corrosions on industrial underfill and present our results. Finally, we present our optimised process to unsolder electronic components which are glued together by an industrial high temperature underfill epoxy, without destroying the targeted electronic components and mobile phones PCB.