Tehnologia BGA-Defecte tipice
The BGA (ball grid array) package type is often used in electronic appliances. The small dimensions, high density of connections, heat dissipation to the board, makes it a good choice in many designs.
In this article I am not going to talk about how to solder or rework a BGA on PCB. That will be another subject. My interest in BGA technology started since I was at university, while I was repairing laptops in my spare time. Below is a drawing with a BGA chip. Note that the bonding wires from DIE to the chip package dissapeared. Instead small tin „bumpers” are used to make connections between DIE and package traces. Many laptops, had problems in the past (2005), because of those bumper connections, especially GPU chips where the demand for power was high. To ensure the amount of power required by a GPU (usually 30-40W) it was necessary @ 30 A (supply voltage was @1v). For such high current, low impedance circuits and connections are necessary. Now, the problem was that in time, because of thermal stress, some power connections were starting to fail, minimizing the power transfer section towards the GPU die. As a result, the power supply was „forced” to cover the voltage drop and was „pumping” higher voltage. Now with increased electrical resistance between GPU die and power supply, more and more power is directly converted to heat which stresses more the remaining connections. The dilation (when in full load) and contraction (when power is off) at last leads to failure of chip and defect device.
I came to this conclusion after few years of study. Usually when a GPU was failing, there was no screen image or image was distorted in a weird way (with special characters and lines)
At the beginning I was just heating up the chip until tin melting temperature was reached. In this way, few bumpers looks like were re-connecting and that was making the chip to work again.. but not for long. In few weeks or months they failed again. The reliable solution was to replace the chip with a new and unused one. That was a proper repair.
Bumpers (microscope view)