Flip Chip Technology: Advancements in Package Assembly

wire bonding techniques

Flip chip technology dates back to the early 1960’s. It was developed by IBM for their SLT modules used in IBM Systems. It was first implemented for commercial application in 1964.  Over the years flip chip technology represented a significant advancement in package assembly. Below is a quick overview of flip-chip technology.

Miniaturization and High Density

Si dies which are assembled using wire bonding, have a few drawbacks. Due to bonding limitations, for commercial application the number of bond pads are only limited to edge space of the four sides of the silicon dies. In most cases no more than 2 rows of bond pads are fabricated to avoid complex wire bonding related issues.

silicon dies

Illustration 1 –  Bond pads at the 4 sides of the die

Due to technological limitations, in order to reliably assemble the package using wire bonding the pad needs to be at least 35um x 35um in size (for 0.7 mil wires)

With flip chip devices on the other hand avoids all of these issues. Advanced micro bump technology now utilizes bump sizes starting at 10um and the full surface of the die can be used for bumping. This ability to use the full surface for bumping makes results in a smaller, more compact in other words a miniaturized IC chip

device with solder bumps

Illustration 2 – WLCSP device with solder bumps spanning full surface of the die

Improved performance

There is a significant distance between the ic chip and the substrate when connected with wires. As you can see in the above picture, the wire needs to travel a few millimeters from the IC to the substrate. But for flip chip devices this is not the case. Flip chip is directly connected to the substrate via bumps. For this reason the flip chip devices has lower inductance, resistance and capacitance compared to wire bonded devices.

Flip chip device connected to the substrate

Illustration 3 – Flip chip device connected to the substrate with under fill and solder resist.

Enhanced Heat Dissipation

Flip chip technology utilizes both top and bottom surfaces effectively. Bottom surface is mounted substrate for interconnects at the same time using underfill to attach and secure the die into the substrate. Top surface of the die and be directly connected to a heat sink. Modern computer processes use this technology for more efficient heat dissipation.

flip chip design and wire bonding design

Illustration 4 – Comparison between flip chip design and wire bonding design.

In conclusion, Flip Chip technology has revolutionized package assembly in the semiconductor industry. Its ability to enable miniaturization, improve performance, and maintain reliability makes it a key technology in the continuing evolution of electronic devices. As the demand for smaller, faster, and more efficient electronics grows, Flip Chip technology will likely continue to see advancements and wider applications.

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