Years ago, plastic (or more accurately epoxy) IC packages had serious reliability problems. They did not handle temperature cycling well, and they were likely to absorb moisture over time. A plastic IC package could absorb moisture while simply sitting on a shelf. A frequent scenario: internal moisture would collect in an internal delamination or other anomaly, then flash into steam when exposed to heat during mounting. The resulting pressure often caused various degrees of damage.
- They are inexpensive and compatible with most standard board-manufacturing processes. The disadvantage of plastic packaging is its poor heat conductivity, limiting its use to applications where the total package power dissipation is typically below 1 watt.
- Ceramic packaging offers better heat conductivity than plastic, and can extend the total package power dissipation to about 5 watts.
- Ceramic also offers improved electrical performance, and has the ability to be hermetically sealed. However, ceramic packaging is relatively expensive compared to plastic.
4. IC damage also stemmed from factors different from temperature. Defects along the lead frame, for example, could permit moisture — and ionic contaminants — to reach and corrode aluminum bond pads on the chip.
5. Ceramic packages have the advantage of hermeticity, which protects vital chip parts from potentially damaging moisture.
6. In many ceramic packages, a protective lid covers the die. The die and lead frame sandwich between two ceramic slabs and are fired at low temperature.
7. Another disadvantage of ceramic packages is their low CTE, which typically does not match the CTE of today's popular PCB materials.
When larger ceramic packages are mounted onto PCBs and subjected to wide temperature extremes, large stresses can build up in the package, causing fracturing of the attachment joints or in the package itself
