It is soldered onto the board using multiple connections, which sit in between the APU integrated circuit and the board. These connections are made out of solder and serve 2 purposes: provides physical mounting to the component as well as electrical connectivity to the board. This type of SMT mounting is called BGA, it stands for Ball Grid Array. As this ball grid array is made completely out of hundreds tiny solder alloy connections they tend to fail from time to time, mostly due to a such high population of them and due heat cycles your PS4 is exposed to during gaming.
This APU is extremely powerful and we all know powerful components on circuit boards do tend to run quite hot. APU is cooled down by a heatsink and fan, however, within itself it still operates at temperatures up to 90C. The problem lies when the substrate temperature is raised and the material expands, however, when console is powered down temperature reduces and all the components retract back to their original positions. Of course, we are talking micro levels here and you won’t see this actual expansion happening. This expansion and retraction isn’t healthy for solder joints and once we add factors, such as moisture accumulation in the air as well as dust contamination these little solder spheres tend to fail by developing micro cracks within ball grid array.
Even if any one of these connections fail, and there are hundreds of them, APU loses its connectivity to the circuit board and your PS4 usually does not turn on at all or malfunctions. Sometimes this will produce artefacts on the screen or video freezes during gaming session.