The drying or curing of organic substrates, adhesives, encapsulants, underfills, inks or coatings is one of the key processes in the manufacturing or assembly of advanced and mature semiconductor packages. The curing process isICA critical step in package manufacturing. It must be as tightly controlled and monitored as any other process step. The effects of improper curing are subtle and often attributed to the material itself or to dispensing and\/or inconsistencies in put operations.
If executed improperly, the curing process often causes downstream yield and reliability issues, not rework costs and delays. However, this critical process step is often overlooked, abused, or simply seen as a risk-free or benign step in the overall assembly process. Often, the responsibility for curing is inherited by process engineers who are assigned to upstream process steps. Perhaps careless attention to curing is a result of the relatively low capital and labor costs traditionally spent in this area.
The curing process requires the same attention and optimization as any other assembly process step.Typical Quality Issuesinclude:
lPollution.Outgassing of volatiles from organic materials in the product during heating can precipitate or deposit on clean surfaces of sub-assemblies in the curing chamber.
lOxidation.Heating processes such as curing or drying may oxidize metallized areas orICPads for electrical interconnections on a die or substrate. Copper is increasingly used forICIn packaging, as an important metal for electrical interconnections. One of the disadvantages of copper is that it tends to form stubborn oxides that are difficult to remove or penetrate, so care must be taken to prevent its formation.
lpressure.Large differences in thermomechanical properties between adjacent materials in the package can lead to high stress gradients that can lead to delamination at the interface and lead to cracking of the package. These conditions can cause electrical interconnects to be lifted or severed, and cause significant damage to the electrical interconnects.ICThe chip itself causes mechanical damage. The stress level varies withICincrease with the increase in die size.