January 11, 2013 at 14:02Non-channel way to fix a hardware error
At the dawn of the Habrahabr era, I was fortunate enough to participate in the development of a complex device, at that time. It was a small 10-layer board jam-packed with electronic components.
After the production of the experimental batch, a serious problem was discovered. An error was found due to which NAND memory did not work. Since NAND was the only option to boot, the device, despite the operability of the remaining components, was completely useless.
It was necessary to solve the problem. When errors are found in the program, patches can be applied to it endlessly. "Hardware" patches in the form of cut tracks and jumpers do not always help to cope with hardware errors. What to do if two rows of pins are mixed up under a BGA chip?
Board revision takes time and money. Since resources were limited, I wanted to do without it. It was necessary to place something under the BGA chip that could fix the pinout. It occurred to me to make an adapter in the form of a double-sided printed circuit board installed under the BGA chip.
It turned out to be an analogue of the now widespread PoP technology . Despite the apparent simplicity, the adapter had to be manufactured in a high accuracy class, as a small diameter of vias and a small width of conductors are required.
There was a desire to make everything quickly, so the production of printed circuit boards was searched at hand. Fortunately, there was one organization that agreed without any guarantees to try to make this adapter.
After a few days, the adapters were ready and they passed the electrical test successfully.
The appearance of the adapter:
For repair it was necessary to follow these steps:
Top view of the repaired circuit board:
Side view of the circuit board:
Fortunately, after completing the operation, all devices without exception worked. After a few years, they are still working for the good of humanity.
Reliability due to such a “patch” was not affected. During operation, the devices are shaken and they heat themselves quite a bit.
After the production of the experimental batch, a serious problem was discovered. An error was found due to which NAND memory did not work. Since NAND was the only option to boot, the device, despite the operability of the remaining components, was completely useless.
It was necessary to solve the problem. When errors are found in the program, patches can be applied to it endlessly. "Hardware" patches in the form of cut tracks and jumpers do not always help to cope with hardware errors. What to do if two rows of pins are mixed up under a BGA chip?
Board revision takes time and money. Since resources were limited, I wanted to do without it. It was necessary to place something under the BGA chip that could fix the pinout. It occurred to me to make an adapter in the form of a double-sided printed circuit board installed under the BGA chip.
It turned out to be an analogue of the now widespread PoP technology . Despite the apparent simplicity, the adapter had to be manufactured in a high accuracy class, as a small diameter of vias and a small width of conductors are required.
There was a desire to make everything quickly, so the production of printed circuit boards was searched at hand. Fortunately, there was one organization that agreed without any guarantees to try to make this adapter.
After a few days, the adapters were ready and they passed the electrical test successfully.
The appearance of the adapter:
For repair it was necessary to follow these steps:
- Using a soldering iron, raise the BGA chip;
- Clean the surface of the board;
- Using a stencil, roll the balls on the underside of the adapter;
- Using a hairdryer, put the adapter on the board;
- Using a stencil to restore the balls on the BGA chip;
- Install the BGA chip on the upper side of the adapter and warm it again with a hairdryer.
Top view of the repaired circuit board:
Side view of the circuit board:
Fortunately, after completing the operation, all devices without exception worked. After a few years, they are still working for the good of humanity.
Reliability due to such a “patch” was not affected. During operation, the devices are shaken and they heat themselves quite a bit.