Limitations with Semiconductor Plastic Packages
July 2022
Decades ago the overwhelming majority of commercial semiconductors were packaged in ceramic packages.
High temperature downhole tools as well as Aerospace and Military hardware benefited from these ceramic packages due to their ability to withstand and dissipate high temperatures. As time and materials technology progressed, semiconductor manufacturers, in their efforts to reduce costs, migrated to various types of plastics to encapsulate the component die and leadframes (component body). Initially, with regards to the hostile environment applications, plastics were a dismal failure. Texas Microelectronics was witness to this. Many companies required their engineers and buyers to exclusively utilize ceramic parts in their products.
As plastic technologies progressed, so did the reliability and high temperature survivability of these components. By the time we reached the 2000’s, more closely to the 2010+ timeframe, plastic component technology had progressed to the point where companies began to use these parts at temperatures ranging from 150 to 175°C, and in some cases briefly up to 200°C.
So what are the limitations with plastic components?
Lifespan and reliability.
Despite the advances in plastic component bodies/encapsulation, with regards to hostile environment and or high-performance applications, there are limitations in the use of plastic components.
Further to the point, the problem of CTE mismatches (Coefficient of Thermal Expansion) between differing materials comes into play. Thermal resistance of the component body material is critical. As the internal die self-generates heat, that heat must dissipate out into, and then out of, the plastic encapsulation material. Plastic is not a good conductor of heat, so that dissipation factor would be considered to be “poor”. Compounding this issue is the CTE mismatch between the silicon die, the wire bonds, and the plastic component body material. The heat dissipated by the die must travel through the plastic material, then from the plastic to free air in the outside world.
When these CTE mismatches reach a certain level, the ability of the different materials to expand and contract equally is exceeded. The primary and typical first failure mode is a disconnection (by shearing effect) of the wire bonds from the die pads, and hence component failure.
Here’s where ceramic or Kovar (metal) packages outperform any plastic packaged part.
Ceramic and Kovar are excellent conductors of heat. The inside of a ceramic or Kovar package contains a cavity where a single die, or multiple in the case of a true Hybrid, is placed. After die placement and the wire bonding process, there is no encapsulation material touching the die, or the wire bonds. The product cavity is sealed in (typically) 100% gaseous Nitrogen, which prevents any oxidation within the component, and eliminates the CTE issues created by plastic materials. The absence of the plastic material surrounding the die and wire bonds enables this device to operate at much higher temperatures, and for a much longer timeframe.
Monolithic die re-packaged in Ceramic
The initial higher cost of a ceramic component or hybrid is easily justified when considering device lifespan and superior performance.
If your company truly wants to excel in the high-performance, hostile-environment markets, then ceramic or Kovar components are the right choice. Texas Microelectronics can get you there.