BGA PCB Manufacturing

Aspherical grid array printed circuit board (BGA PCB) is a surface-mount encapsulated PCB designed for integrated circuits. The use of BGA boards for surface mounting is a permanent application, for example, in devices such as microprocessors. These are disposable printed circuit boards and cannot be reused. The BGA board has more interconnect pins than ordinary PCBs. Each point on the BGA board can be welded independently. The entire connections of these PCBs are dispersed in a uniform matrix or surface mesh. These PCBs are designed to make the entire bottom easy to use, not just the surrounding area.

The BGA-encapsulated pin is much shorter than an ordinary PCB because it has only a perimeter-type shape. For this reason, it can provide higher speed and better performance. BGA welding requires precise control and is more often guided by automated machines. This is why BGA devices are not suitable for socket installation.

BGA is a common component on PCB. Generally, CPU, North Bridge, South Bridge, AGP chip, card bus chip, etc. are mostly packaged in the form of BGA. In short, 80% of high-frequency signals and special signals will be pulled out of this type of package. Therefore, how to handle the routing of the BGA package will have a great impact on important signals.

Generally, small parts surrounding BGA can be divided into several categories according to the priority of importance:

1. Bypass.

2. Clock terminal RC circuit. (in the form of series resistance and row group, for example, memory bus signal)

4. EMI RC circuit (in the form of damping, and pull height; for example, USB signal).

5. Other special circuits (special circuits added according to different chips; such as temperature sensing circuit of CPU).

6. Small power supply circuit group below 40mil (in the form of C, l, R, etc.; this circuit often appears near AGP chip or chip with AGP function, and different power supply groups are separated through R and L).

7. pull low.

8. General small circuit group (in the form of R, C, Q, u, etc.; no wiring requirements).

9. pull height RP.

BGA PCB package design

The circuits of items 1-6 are usually the focus of placement. They will be arranged as close to BGA as possible, which needs special treatment. The circuit of item 7 is second in importance, but it will also be arranged closer to BGA. 8. Item 9 is a general circuit, which belongs to the signal that can be connected.

Relative to the priority of the importance of small parts near BGA, the requirements on routing are as follows:

1. By pass = > when it is on the same side as chip, connect it directly from chip pin to by pass, and then pull it out by pass to connect via to plane; When it is different from the chip, it can share the same via with VCC and GND pin of BGA. The line length should not exceed 100ml.

2. RC circuit of clock terminal = > there are requirements for line width, line distance, line length, or package GND; The route shall be as short and smooth as possible, and shall not cross the VCC separation line as far as possible.

3. damping =>

There are requirements for line width, line spacing, line length, and grouping routing; The routing shall be as short and smooth as possible. The routing shall be group by group, and other signals shall not be mixed.

4. EMI RC circuit = > there are requirements for line width, line spacing, parallel routing, package GND, etc; Complete according to customer requirements.

5. Other special circuits = > there are requirements for line width, package GND or routing clearance; Complete according to customer requirements.

6. Small power supply circuit group below 40mil = > wire width and other requirements; Try to finish with the surface layer, reserve the inner space completely for the signal line, and try to avoid unnecessary interference caused by the power signal passing through the layer above and below the BGA area.

7. Pull low R, C = > no special requirements; The routing is smooth.

PCB and Embedded designers always require the minimum number of circuit board layers. In order to reduce costs, the number of layers needs to be optimized. However, sometimes the designer must rely on a certain number of layers. For example, in order to suppress noise, the actual wiring layer must be sandwiched between two grounding plane layers.

In addition to the design factors inherent in the embedded design using a specific BGA, the design generally includes two basic methods that the embedded designer must adapt to correctly detour the signal routing from the BGA: dog bone fanout (Fig. 1) and via in the pad (Fig. 2). The dog bone fanout is used for BGA with ball spacing of 0.5mm and above, while the via in the pad is used for BGA and micro BGA with ball spacing of less than 0.5mm (also known as ultra-fine spacing). Spacing is defined as the distance between the center of a ball of BGA and the center of adjacent balls.

Through-hole fan out the method in welding pad

It is important to understand some basic terms related to these BGA signal wiring technologies 'Through-hole' refers to the pad with charged planting hole, which is used to connect the copper wire of one PCB layer with the copper wire of another layer. The high-density multilayer circuit board can be used to blind holes or buried holes, also known as micro vias. Only one side of the blind hole is visible, and neither side of the buried hole is visible.

BGA PCB Wiring

Three different boundaries related to BGA

The first step is to determine the via size required for the BGA fan out. The via size depends on many factors: component spacing, PCB thickness, and the number of wires routed from one area or perimeter of the via to another. The perimeter is a matrix, square, or polygonal boundary that surrounds the BGA.

The second step is to define the line width from BGA to the inner layer of the circuit board. There are many factors to consider when confirming linewidth. The minimum space required between routes limits the BGA detour wiring space. It is worth noting that reducing the space between wires will increase the manufacturing cost of the circuit board.

Third, the designer must maintain impedance matching as required and determine the number of wiring layers used to completely decompose the BGA signal. Next, use the top layer of the circuit board or the layer where the BGA is placed to complete the BGA outer ring wiring.

The remaining parameters are distributed on the internal wiring layer. The number of layers required to complete the whole BGA wiring is estimated according to the number of the internal wiring of each channel. After the outer ring is wired, lay another circle. Then route the subsequent inner rings in the same way until all BGA wiring is completed.

Advantages of BGA packaging

BGA encapsulation has many advantages, but only the top professionals are detailed below.

1. BGA encapsulation effectively uses PCB space: BGA encapsulation uses smaller components and smaller space occupied. These packages also help to save enough space for customization in the PCB to improve its effectiveness.

2. Improvements in electrical and thermal performance: The size of BGA packages is very small, so these PCBs have less heat loss and are easy to achieve the dissipation process. Whenever the silicon wafer is mounted on the top, most of the heat is transferred directly to the grid. However, when the wafer is mounted at the bottom, the wafer is connected to the top of the package. That's why it's considered the best choice for cooling technology. There are no bendable or fragile pins in the BGA package, which increases the durability of these PCBs while ensuring good electrical performance.

3. Improve manufacturing profitability by improving welding: BGA-encapsulated pads are large enough to make them easy to weld and easy to operate. Therefore, it is easy to weld and handle to make it very fast. The larger pads of these PCBs can also be easily reworked if needed.

4. Reduce the risk of damage: BGA packages are solidified and therefore provide strong durability and durability under all conditions.

5 of. Cost reduction: These advantages help reduce the cost of BGA packaging. Effective use of printed circuit boards provides further opportunities to save materials and improve thermoelectric performance, helping to ensure high-quality electronic products and reduce defects.