If you are not sure about the term "FlipChip", this guide will help you better understand the technology of FlipChip packaging (also known as flip chip packaging).
The FlipChip package technology has been around for 3-4 decades, as its original role as a solution for large numbers of batteries and requiring high performance packages. At first, most FlipChip package applications were SoCs with a large battery count (including more than 700 batteries), which the typical Wire-Bond BGA package could not handle properly. In addition, some SoCs incorporate high-speed (including RF) interfaces that wirebond (wiring - the process of connecting the conductors on the chip base to the very thin wires from the circuits on the chip) may not support. due to high wire inductance.
Demand for FlipChip packages has increased over the past decade and is driven by the mobile market where package size and signal performance play a crucial role.
Today, the FlipChip package technology offers a wide range of benefits including: Large battery count, high signal density, better spreading power, low signal inductance and good power / ground connection. FlipChip packages are quite popular these days and you can find them in compact devices such as high-end mobile phones.
Basically, the name FlipChip describes the method used to connect a semiconductor die to the chip base. In a FlipChip package, the molds bounce and then flip onto the chip base, hence the name FlipChip.
Thanks to the fact that the bumpers are distributed across the entire chip, not just on the edge of the mold, pads can be placed all over the mold surface. This allows designers to place more pads per mold, reducing chip size and optimizing signal integrity.
The chip base provides connection to an external PCB via solder ball. Chip base size, number of layers and material properties have a direct impact on the total cost. In some cases, the chip base can be the most expensive element in the FlipChip package.
The bumpers are located directly on the I / O pads and thus, they connect the mold to the base. After bumping (bumping is an advanced wafer-level processing technology, where solder ball / bump is formed on wafers), the wafer is broken down and finally, the molds flip over the base. chip. The bumpers connect the die and chip base together into a single package.
Chip base technology
The FlipChip chip base is a small PCB inside the package and very similar to any other PCB. The difference is that the chip base size is much smaller than most PCBs you've seen.
The chip base design includes the layout of all signals from the outside of the package to the bump pads.
The chip base can be fabricated using many different materials: Laminate wood, porcelain, etc. The rules for chip base layout design are different from each supplier.
The chip base can consist of multiple layers ranging from 2-18 layers to allow routing of all signals.
Wafer Bumping Technology
The bump wafers provide a connection between the die and the chip base, through low inductance and resistance, as well as reliable, high-quality manufacturing materials.
Wafer bump can be constructed from eutectic, lead-tin, unleaded, high-lead or Cu pillar technology. The assembly dimensions and bump spacing are not the same.
Assembly process of FlipChip
During the final processing step of the wafer bumping process, bumpers placed on the chip pads can be found on the top of the wafer. In order for the chip to be connected or attached to the base, the mold is flipped and aligned with the pads on the base.
There are 6 steps in the FlipChip creation process, providing it with considerable flexibility when connecting devices.
Advantages and disadvantages of FlipChip
FlipChip packages have advantages and disadvantages, stemming from the assembly method of making a chip much more compact than previous wirebond solutions. Because the chip is directly connected to the circuit board, the conductor is shorter, creating less inductance. This means the devices can now transmit the signal at significantly higher speeds, while dissipating heat more efficiently.