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.

除了传统的高温共晶焊接之外，使用底部填充环氧树脂将电子组件胶粘到PCB（内存，CPU，加密芯片）现在已经成为手机制造商（例如Apple，BlackBerry和Samsung）的标准。当前，该技术是保护组件免受各种机械应力并提高可靠性的最佳解决方案。不幸的是，传统的技术（切屑或研磨）已无法应用于未填充的部件而又不破坏它们或不移动外围电子部件的情况。这些部件的移动使电路板无法使用，或者需要花费大量时间进行昂贵的维修和特定的硬件。

在数字取证领域中，酸及其用途可能是令人感兴趣的。首先，它们可用于在读取芯片之前对电子组件的包装进行解封装（通过芯片上的物理堆放），或通过硅芯片的微读取技术对安全系统进行反向工程。而且，正如我们在本文中所显示的，随着最新一代手机的到来，如果调查人员希望使用经典的切屑方法（或合法移植损坏的手机）来对使用底部填充环氧树脂的手机使用酸混合物，则可能会引起关注。它们一起覆盖了相邻的组件（CPU，内存，电容器等）。

这项工作介绍了一种称为“底部填充酸腐蚀”的新方法。所提出的方法是基于使用加热到各种温度的酸的不同混合物。我们定量研究了影响工业底部填充酸腐蚀效率的因素，并提出了我们的结果。最后，我们提出了一种优化的工艺，可以对通过工业高温底部填充环氧树脂胶粘在一起的电子元件进行拆焊，而不会破坏目标电子元件和手机PCB。