Package Cracking (Page 3 of 3)

Ceramic Package Cracking  

Ceramic package cracking is the occurrence of fracture(s) (see Fig. 2) anywhere in or on a ceramic package.  Ceramic cracks can be caused either by thermomechanical or by purely mechanical means.  The distinction between cracks due to thermomechanical causes and those due to purely mechanical causes is not always easy though.

A sudden and large change in package temperature causes 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 ceramic cracks during solder dipping. Packages with castellations are vulnerable to this mechanism, since the expansion of the metal inside the castellation during solder dipping tends to split the ceramic around it, initiating a crack that can easily propagate across the package.

Impact loading is the most common source of package cracks in ceramic DIPs. Impact loading is the sudden application of force on a body.  Ceramic units inside metal tubes can easily crack if the tube is accidentally dropped to the floor, especially if the floor is made of concrete.  End-to-end banging from tube-to-tube or equipment rail-to-rail transfers can also result in cracks.  High-pressure air drying that propels one unit into another has even been found to cause base-cap separation.  Data also suggest that improper tube packing can lead to microcracks that can propagate through subsequent handling. Massive units dropping to any hard surface of an equipment can also suffer microcracks.

Figure 2. Photo of a cerdip with a corner

package and seal glass crack

Poor package design or condition can also cause package cracks.  Sidebrazed units with rhino horns are highly vulnerable to package cracking and chipping during end-to-end collisions.  Some sidebrazed packages need their plating bars removed by grinding.  The grinding process can produce both a recession and a protrusion at the package end.  Such a protrusion is called a rhino horn, and acts as a stress concentrator when a unit collides with another during tube-to-tube or rail-to-rail transfers.  This stress concentration can result in cracks that originate that the corner of the package where the rhino horn is present. Package defects like microcracks, voids, geometrical aberrations, and the like all act as stress concentrators.

Poor equipment set-up or debris under the package during back-end mechanical operations like lead trimming may possibly cause cracks, although this has become rare over the past years.

Base-cap separation is the detachment of the cap from the base of a cerdip package due to high-impact shearing between the cap and base.  Base-cap separation is basically a failure of the glass seal of the package, even though the impact loading occurs at the ceramic package itself.  Base-cap separation may therefore be defined also as a total fracture of the seal glass all around the seal path, resulting in the separation of the cap from its base.

The most common cause of base-cap separation is end-to-end banging. Units with excessive longitudinal mismatch or offset between the base and cap are therefore more susceptible to exhibit this failure. The use of extremely high pressure for blow-drying units can propel units into one another, and lead to base-cap separation.  Improper tube-to-tube or rail-to-rail transfers can also lead to base-cap separation. Units inside metal tubes that are dropped accidentally to a concrete floor may also suffer base-cap separation.

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