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Friday 17 February 2012

bga chip repair

bga_gpu
PROBLEM
Last week when I turned on my laptop HP dv2750, there were multiple screens appearing on the display instead of one screen, and some times the screen even didn’t appear. I reinstalled and updated the nvidia drivers (as it has nvidia 8400GM) assuming something might be wrong with the drivers, but when the notebook restarted the multiple screens appeared right from the time it restarted, i.e. there were six boot screens, instead of one. I logged on to the HP website and updated my bios, but the problem didn’t solve. I ran the system restore, but that was also useless. I searched for the problem on the net and found that there is a die-packaging manufacturing defect in nvidia GPU of G84 and G86 which was officially announced by NVIDIA. These nvidia GPU are in most of dv2000/dv6000 series of HP pavilion laptops
Solution:
My laptop’s warranty expired last and was also not covered by HP Limited Warranty Service Enhancement. I talked to HP, they confirmed it as a hardware malfunctioning of nvidia GPU (Graphics Processing Unit), but refused to repair it free of cost (estimated cost by HP was $300+shipping charges). I being a student couldn’t afford that much. As I was out off options so I decided to get it repaired locally.
The local techinian immediately identified the problem. Actually the problem is in the Ball Grid Array (BGA) of Nvidia GPU. With the passage of time (approximately 1 year), the Ball Grid Array Soldering of the GPU gets damaged due to heating. When it gets damaged, some pins of the GPU loses the contact with the motherboard, and hence displays nothing. The local technician told that there are two methods to repair it
  1. Temporary Repair
  2. Permanent Repair
Temporary Repair
In temporary repair he would air heat the GPU, as a result the soldering balls in BGA would get settled and connections would be re-established, but the problem may show up again in a week or a month.
Permanent Repair
The permanent repair was more risky then the temporary one. There is 80% chance of getting it permanently repaired and 20% chance of permanent damage. I took the risk and finally the problem was resolved. In this repair the GPU was be detached (Desoldered) from the motherboard, and the new balls were  made for BGA and the GPU was again fixed to the motherboard. When the laptop was turned on, the problem was actually resolved. The technician told that he has repaired many dv2000/dv6000 notebooks with the same problem, and none have reported the issue to him again.
BGA
Ball Grid Array are surface mount packages (smd) that uses metal balls and spheres to provide electrical interconnection
bga1
The problem is the same as reported in XBOX 360′s GPU’s  BGA. Another BGA is shown below
rrod_voiding
Note: If you have any queries, post them in the comment section below

Ball Grid Arrays in Printed Circuit Board Assembly

The complex maze of circuitry found on printed circuit boards actually serves a somewhat straightforward purpose. Through electrical pathways known as “traces,” a print circuit board (or PCB) connects various electronic components on a single substrate. Its surface contains integrated circuits, such as microprocessors, while the underside is printed with a lattice of traces. Completed PCBs are themselves components within larger apparatuses, such as computers or appliances, and effective PCB assembly is important for these machines to function properly. When evaluating PCB production, one should keep in mind that the method by which components are attached to a board’s surface can influence its stability, durability, and design efficiency.

A pin-grid array (PGA) is the former standard for packaging integrated circuits on a board, but many manufacturers now use the more recently developed ball grid array (BGA) design. A PGA uses a square arrangement of metallic pins inserted into complementary holes on the circuit board to mount components. In a BGA, these pins are replaced with metal balls composed of solder, which are attached to the laminated underside of the unit. In both cases, the array must be soldered into place to secure the component to the board.

 Ball Grid Array Specifications

Components of a Ball Grid ArrayTo better understand the unique properties of a ball grid array, it may be helpful to visualize an integrated circuit designed with the BGA. A die, such as a chip or processor, is attached to one side of a plastic or ceramic slab that serves as the substrate. This die is usually connected to the slab via gold or aluminum wire bonding, or mounted directly as a “flip-chip.” A shielding mold is used to protect it and hold it in place. Solder balls are fastened to the other side of the substrate, which is laminated. The substrate also contains internal traces to connect the die to the ball grid. When the component is ready to be attached to the printed circuit board, it is referred to as a “package.”

Printed circuit board manufacturers typically use solder to fasten the package to a circuit board in both BGA and PGA formats. Standard operations employ surface-mount technology (SMT) robotic arms to position the component in its designated location on the circuit board. The PCB usually has a series of copper pads on its surface patterned to match the ball grid array on the component. Once the robotic arm positions the package on the copper pads, it is heated to create the desired soldering effect. To achieve this, the PCB is sent to a reflow oven, where it is conveyed through several high temperature zones, followed by a cooling zone. During this process, the solder melts, cools, and solidifies, leaving the component attached to the circuit board.

Advantages of the BGA

A major benefit of using BGAs results from the relatively high density of balls on the component substrate. The closeness of the balls elevates interconnection, which in turn raises the efficiency of the packaging process. High density also reduces the space a component occupies on the printed circuit board, allowing for more effective use of board area. In a pin-grid array, increasing the volume of pins reduces the distance between them and runs the risk of accidental bridging during the soldering process, which disrupts the connection between the component and the PCB. Accidental bridging is less of a concern for BGAs because the balls are composed of solder, so heating will not affect their functionality.

Packaging a BGA onto a circuit board is also relatively easy due to the makeup of the balls. The solder balls are applied with automated precision during manufacturing, and require only heating in order to melt and adhere to the PCB. This eliminates the chances of component damage resulting from a separate soldering process, such as that used for metal leads in a pin-grid array. In addition, the surface tension between the balls and the circuit board helps keep the package in its designated place during adhesion.

Components packaged with a ball grid array have a lower incidence of overheating and thermal damage due to the reduced heat resistance between the BGA and the circuit board. A large amount of the heat generated by an operating component dissipates into the circuit board because BGA units remain in close proximity to the board and provide thermal channels within the substrate to enhance heat-flow away from the die. The nearness of the component to the board also helps reduce signal distortion during high-speed work, subsequently boosting electrical performance.

Disadvantages of the BGA

PCB board versus BGA One of the drawbacks of a ball grid array package stems from the inflexibility of the balls. After soldering, the array forms a rigid, unbendable bond between the board and the component. This stiffness allows physical stress, such as vibration, or heat expansion pressure to be transmitted back into the die. Such strain can degrade the package’s reliability or even render it nonfunctional.

In addition, the close proximity between the component and the board can make quality assurance and inspection of a completed PCB quite difficult. Flaws can be identified using sophisticated infrared devices and microscopes, and repaired through vaccum treatments and ball replacement. Manufacturers may want to consider the cost-effectiveness of using a ball grid array compared to the price of repairing, or even recalling, a damaged product.

PBGA

Although the ball grid array has a number of useful applications in PCB construction, it may not be suited for certain work. In cases where neither a BGA nor a PGA will suffice, consider a commonly used alternative, such as a plastic ball grid array. A plastic ball grid array (PBGA) is a variation on the standard BGA, featuring a plastic-coated body, a glass-mixture laminated substrate, and etched copper traces. It exhibits improved temperature stability and uses preformed solder balls, which are later reshaped to accommodate the final package design.

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