Contaminants on the surface of the leadframe, die, or die paddle can prevent good adhesion with the plastic material and lead to delamination. The use of incorrect leadframe texture, dimensions, and design can also reduce adhesion strength. The use of molding compounds with excessive mold release agent can also lead to delamination. Excessive mismatches between the thermal coefficient of the plastic and those of the leadframe, die, and die attach material can also result in delamination. Insufficient bond line thickness due to inadequate die attach material dispensing may result in cohesion failure within the die attach material, which can lead to package delamination and even cracking.

Packages of plastic surface mount devices (SMDs) may delaminate internally, if not crack, because of the intense pressure build-up generated by the vaporization of the internal moisture inside the package during solder reflow (see Plastic Package Cracking for more details). These type of delamination occurs between the die and/or die paddle and the plastic, and always precedes package cracking.

Seal Cracking

Solder seal cracking is the occurrence of fracture(s) (see Fig. 3) anywhere in the solder seal of a ceramic package that uses a combo lid, e.g., sidebrazed, LCC, and JLCC packages.  Most solder seal cracks may be attributed to defects in the seal, which in turn are due to a poor solder sealing process. Mechanical defects such as voids, incomplete coverage, and poor filleting, and chemical defects such as seal oxidation or corrosion, weaken the seal and make it susceptible to cracking.

A sudden and large change in package temperature can lead to solder seal cracking too, especially if there are defects in the seal.  Such sudden changes in temperature cause tremendous thermomechanical stresses at the ceramic-to-metal interfaces of the package, due to large differences between the coefficient of thermal expansion of ceramic and those of the metals used in the package. For instance, inadequate pre-heating can result in solder seal cracks during solder dipping.

Poor package design or condition can also cause solder cracks. The use of insufficient seal path widths or inadequate seal preform can result in narrow seals, which are more likely to crack than a robust seal.

A lot of solder seal cracks are just secondary effects of package cracking.  Interestingly, some seal cracks even look worse than the primary failure mechanism, namely package cracking, which can be invisible without staining the package. A thorough check of the package for microcracks must therefore be conducted everytime a solder seal crack is analyzed, no matter how gross the seal damage looks.

Seal glass cracking is the occurrence of fracture(s) anywhere in the seal glass of a Cerdip package.  Most seal glass cracks may be attributed to impact stresses.  A common cause of impact stresses is end-to-end banging between units from improper handling of tubes.  Advanced stages of seal glass cracking from impact stresses can lead to base-cap separation (see separate article on 'Base-Cap Separation').

Seal glass cracking may also be aggravated by seal glass defects such as base-cap mismatches and offsets, glass overcure, glass undercure, and excessive glass etching from the cleaning processes prior to leadfinish.