FOPLP and chip cooling: why semiconductor packaging is becoming a thermal battleground

As transistor density and power consumption rise, semiconductor packaging is no longer just a protective shell. It has become part of the chip’s thermal solution.

Huatian Technology says it has developed end-to-end thermal design and simulation capabilities for fan-out packaging, allowing heat management to be considered throughout the FOPLP process rather than addressed after assembly. 8

The promise of fan-out panel-level packaging (FOPLP) is a shorter and more controllable route from the die to the package, circuit board and cooling system. That could benefit devices with high power density. It does not, however, prove that FOPLP will deliver better thermal performance in every application.

Why package-level thermal design matters

More computing capability is being concentrated into smaller die areas. As a result, heat must escape from a more restricted region, often creating hotspots and reducing the available reliability margin.

A chip’s junction temperature is determined by the entire heat path—not just the silicon. That path can include the die attach and mold compound, redistribution layers (RDL), the package surface, the PCB, thermal-interface materials, a heatsink and the surrounding airflow.

If that route has high thermal resistance or concentrates heat in specific areas, the device may operate at a higher temperature. Sustained thermal stress can also contribute to interconnect fatigue, material delamination, coefficient-of-thermal-expansion mismatch and package warpage.

The limits of SOP, QFP and QFN packages

Traditional SOP and QFP packages typically move much of their heat through leads and a leadframe. This often creates a longer and more constrained thermal path. Huatian contrasts those conventional structures with FOPLP, which is designed without a traditional package substrate and with a shorter route for heat flow. 6

QFN packages need a more nuanced assessment. An exposed-pad QFN or power-QFN can provide an effective thermal path into the PCB. Its performance depends on the leadframe geometry, thermal pad, copper area, via design and the board’s ability to spread heat.

That means it would be inaccurate to describe every QFN package as thermally inadequate. A QFN may be entirely suitable at one power level and insufficient at another. The relevant question is how the package and board perform together in the intended system.

How FOPLP could improve heat management

Fan-out packaging routes the die’s connections outward through RDL rather than relying exclusively on a conventional package substrate. This supports high-density interconnects and, compared with some traditional architectures, can reduce electrical inductance. 4

A typical FOPLP structure combines:

• no conventional package substrate;
• high I/O density;
• a thin profile;
• RDL that supports electrical interconnection and can also contribute to heat spreading; and
• coordinated optimization of materials, layout and package geometry.

Fraunhofer IZM describes fan-out as a substrate-free package technology with significant miniaturization potential and low thermal resistance. TSMC’s InFO platform also illustrates how high-density RDL can support mobile and high-performance computing applications. 1213

But thinness and high I/O density do not automatically translate into better thermal performance. The benefit depends on whether the copper routing, mold compound, die backside, heat spreader and PCB form an effective heat path. A substrate-free design can shorten the route, but the rest of the system still determines how efficiently heat leaves the package.

Different thermal priorities across applications

Fan-out packaging has already been used in mobile and wireless applications and is expanding into automotive and medical systems. 1 High-density fan-out platforms are also being positioned for mobile products and high-performance computing. 13

The thermal value of FOPLP varies by application:

• Mobile devices: Thinness is a major priority. Heat must be spread through a compact chassis, often without room for a large heatsink.
• Automotive electronics: Packages must withstand repeated thermal cycling and wide temperature swings over long operating periods.
• High-performance computing: Total power is much higher. Even an efficient package may require a lid, cold plate or other external cooling infrastructure. FOPLP does not replace system-level thermal engineering.

Thermal resistance is not the same as a characterization parameter

JEDEC thermal metrics are meaningful only when considered alongside the specific test conditions under which they were measured. A theta value represents a defined thermal-resistance path. Psi parameters, by contrast, are characterization metrics that correlate junction temperature with a measurable temperature at the top of the package or on the board.

RθJC, for example, describes the junction-to-case path when heat is deliberately directed toward the case surface, such as during a test involving a thermal plate or heatsink. It does not necessarily represent heat flow on a real application board, where power may be divided between the package top, PCB, solder balls or leads and the surrounding environment.

For that reason, the following equation should not be treated as a universal way to estimate operating junction temperature:

Tj = Tc + P × RθJC

Texas Instruments notes that ΨJT and ΨJB can often be more useful for modern board-mounted applications. 13 When the measurement conditions are appropriate, engineers may use relationships such as:

Tj ≈ Ttop + P × ΨJT
Tj ≈ Tboard + P × ΨJB

ΨJT and ΨJB are not fundamental one-dimensional thermal resistances. They are characterization parameters whose values depend on the test setup, layout and system conditions. The distinction matters because using the wrong metric can produce a misleading estimate of junction temperature.

What Huatian’s “full-process” capability means

According to the company’s description, Huatian’s approach covers material selection, wiring design and package structure, using multiphysics simulation to improve heat dissipation and long-term reliability. 8

In practical engineering terms, such a workflow would need to combine:

• selection of mold compound, die-attach materials and thermal-interface materials;
• optimization of the thickness and placement of copper RDL for heat spreading;
• identification and reduction of hotspots;
• joint analysis of thermal conduction and electrical power losses;
• evaluation of warpage and coefficient-of-thermal-expansion mismatch; and
• assessment of fatigue during thermal cycling.

Large, thin panel-level structures make thermomechanical analysis especially important. Research on FOPLP has examined material behavior and deformation during cooling, while warpage and die shift remain recognized reliability challenges. 3

The objective is therefore broader than simply lowering a package’s headline thermal-resistance number. The design must balance heat flow, electrical performance, manufacturability and mechanical reliability across the package’s expected lifetime.

The bottom line: the claim still needs measurements

FOPLP gives Huatian a way to address heat at the architectural level. The company can reduce unnecessary structural layers, use dense RDL for interconnection and potential heat spreading, and optimize materials and geometry before the package is finalized. These are reasonable potential advantages of fan-out packaging and align with the technology’s broader direction. 812

They do not, by themselves, establish a specific thermal improvement for a Huatian product. The available material does not provide independently verified figures for thermal resistance, junction temperature or product lifetime.

The meaningful test is measured junction temperature and reliability under the actual application conditions: the specific PCB, power distribution, cooling boundary, airflow and thermal-cycle profile.

The key question is therefore not simply, “What is the package’s RθJC?” It is whether the complete system can keep the chip within its temperature limits throughout its operating life.