Method of making a semiconductor chip assembly with a bump/base heat spreader and a cavity in the bump

Abstract

A semiconductor chip assembly includes a semiconductor device, a heat spreader, a conductive trace and an adhesive. The heat spreader includes a bump, a base and a flange. The conductive trace includes a pad and a terminal. The semiconductor device extends into a cavity in the bump, is electrically connected to the conductive trace and is thermally connected to the bump. The bump extends from the base into an opening in the adhesive, the base extends vertically from the bump opposite the cavity and the flange extends laterally from the bump at the cavity entrance. The conductive trace is located outside the cavity and provides signal routing between the pad and the terminal.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation-in-part of U.S. application Ser. No. 12 / 616,773 filed Nov. 11, 2009 and a continuation-in-part of U.S. application Ser. No. 12 / 616,775 filed Nov. 11, 2009, each of which is incorporated by reference. This application also claims the benefit of U.S. Provisional Application Ser. No. 61 / 330,318 filed May 1, 2010 and U.S. Provisional Application Ser. No. 61 / 350,036 filed Jun. 1, 2010, each of which is incorporated by reference.[0002]U.S. application Ser. No. 12 / 616,773 filed Nov. 11, 2009 and U.S. application Ser. No. 12 / 616,775 filed Nov. 11, 2009 are each a continuation-in-part of U.S. application Ser. No. 12 / 557,540 filed Sep. 11, 2009 and a continuation-in-part of U.S. application Ser. No. 12 / 557,541 filed Sep. 11, 2009.[0003]U.S. application Ser. No. 12 / 557,540 filed Sep. 11, 2009 and U.S. application Ser. No. 12 / 557,541 filed Sep. 11, 2009 are each a continuation-in-part of U.S. application Ser. No. 12...

AI Technical Summary

Benefits of technology

[0034]The adhesive can contact the bump and the dielectric layer in a gap in the aperture between the bump and the substrate, extend across the dielectric layer in the gap and contact the base, the dielectric layer and the terminal outside the gap. The adhesive can also cover the base outside the bump in the first vertical direction, cover the substrate in the first vertical direction and cover and surround the bump in the lateral directions. The adhesive can also conformally coat the sidewall of the bump, a surface portion of the base that is adjacent to and extends laterally from the bump and faces in the first vertical direction and a surface of the dielectric layer that faces in the first vertical direction. The adhesive can also fill the space between the bump and the dielectric layer, between the base and the flange and between the base and the substrate.

[0079]The present invention has numerous advantages. The heat spreader can provide excellent heat spreading and heat dissipation without heat flow through the adhesive. As a result, the adhesive can be a low cost dielectric with low thermal conductivity and not prone to delamination. The bump and the flange can be integral with one another, thereby enhancing reliability. The bump can have a tapered sidewall and a highly reflective surface layer. As a result, the bump can focus the light generated by an LED chip mounted on the bump within the cavity, thereby enhancing the light output. Furthermore, the cavity can provide a well-defined space for a color-shifting encapsulant deposited on the LED chip. As a result, the color-shifting encapsulant can be dispensed into the cavity in a small consistent amount, thereby enhancing optical performance and reducing cost. The base can include a selected portion of the conductive layer laminated to the dielectric layer, thereby enhancing reliability. The adhesive can be sandwiched between the bump and the substrate, between the base and the substrate and between the flange and the substrate, thereby providing a robust mechanical bond between the heat spreader and the substrate. The conductive trace can provide signal routing with simple circuitry patterns or flexible multi-layer signal routing with complex circuitry patterns. The conductive trace can also provide vertical signal routing between the pad and the terminal using a plated through-hole that extends through the adhesive and the dielectric layer. Furthermore, the plated through-hole can be formed after the adhesive is solidified and remain a hollow tube or be split at a peripheral edge of the assembly. As a result, a solder joint subsequently reflowed on the terminal can wet and flow into the plated through-hole without creating a buried void in the solder joint that might otherwise occur if the plated through-hole is filled with the adhesive or another non-wettable insulator, thereby increasing reliability. The base can provide mechanical support for the substrate, thereby preventing warping. The assembly can be manufactured using low temperature processes which reduces stress and improves reliability. The assembly can also be manufactured using well-controlled processes which can be easily implemented by circuit board, lead frame and tape manufacturers.

Problems solved by technology

Semiconductor devices are susceptible to performance degradation as well as short life span and immediate failure at high operating temperatures.

The heat not only degrades the chip, but also imposes thermal stress on the chip and surrounding elements due to thermal expansion mismatch.

LEDs include high power chips that generate high light output and considerable heat.

Unfortunately, LEDs exhibit color shifts and low light output as well as short lifetimes and immediate failure at high operating temperatures.

Furthermore, LED light output and reliability are constrained by heat dissipation limits.

However, since the plastic and the dielectric layer typically have low thermal conductivity, the PBGA provides poor heat dissipation.

However, since the lead frame type interposer has limited routing capability, the QFN package cannot accommodate high input / output (I / O) chips or passive elements.

However, manually dropping the heat slug into the central opening is prohibitively cumbersome and expensive for high volume manufacture.

Furthermore, since the heat slug is difficult to accurately position in the central opening due to tight lateral placement tolerance, voids and inconsistent bond lines arise between the substrate and the heat slug.

The substrate is therefore partially attached to the heat slug, fragile due to inadequate support by the heat slug and prone to delamination.

The heat slug is therefore non-planar and difficult to bond to.

As a result, the assembly suffers from high yield loss, poor reliability and excessive cost.

However, the insulating layer sandwiched between the metal core layer and the PCB limits the heat flow to the PCB.

As a result, the heat spreader releases the heat by thermal convection rather than thermal conduction which severely limits the heat dissipation.

Consequently, the substrate is unbalanced and wobbles and warps during manufacture.

This creates enormous difficulties with chip mounting, wire bonding and encapsulant molding.

Furthermore, the expanded base may be by the encapsulant molding and may impede soldering the package to the next level assembly as the solder balls collapse.

As a result, the package suffers from high yield loss, poor reliability and excessive cost.

However, the electrical contacts are difficult to mount on the insulating layer, difficult to electrically connect to the next level assembly and fail to provide multi-layer routing.

Conventional packages and thermal boards thus have major deficiencies.

For instance, dielectrics with low thermal conductivity such as epoxy limit heat dissipation, whereas dielectrics with higher thermal conductivity such as epoxy filled with ceramic or silicon carbide have low adhesion and are prohibitively expensive for high volume manufacture.

The dielectric may delaminate during manufacture or prematurely during operation due to the heat.

The substrate may have single layer circuitry with limited routing capability or multi-layer circuitry with thick dielectric layers which reduce heat dissipation.

The heat spreader may be inefficient, cumbersome or difficult to thermally connect to the next level assembly.

The manufacturing process may be unsuitable for low cost, high volume manufacture.

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