is the process of encapsulating a
package, usually by capping or putting a lid over the base or body of
The method of
sealing is generally dependent on the type of package. Ceramic DIPs, or
cerdips, are sealed by topping the base of the package with a
using seal glass. Other ceramic packages such as sidebrazed
packages, LCC's, and PGA's are sealed by covering the package with a
through solder sealing. A sealing
(see Fig. 1) is used to expose the packages to the high temperatures
needed to achieve proper sealing.
like any glass, is a supercooled liquid which exhibits tremendous
viscosity when cooled below its glass transition temperature. A
seal glass may be classified as vitreous or devitrifying.
glass are relatively transparent and can be reworked repeatedly without
degradation in its properties.
glass can no longer be reworked after crystallizing upon cooling.
are added to seal glass to control the thermal expansion of the glass.
cerdip glass sealing process consists of the following steps in its
sealing profile: 1) organic burn-off/ougassing; 2) glass
densification or softening of glass; 3) glass profile formation (around
350 deg C); 4) chemical bonding between glass and ceramic (around 420
deg C); 5) annealing; and 6) cooldown.
than heat-up because this affects the final properties of the glass more
is used to join the metal header and metal cap of metal cans. A
specially-designed welding machine is used to deliver the high currents
needed to weld the metal header and metal cap at their interface.
Figure 2 shows an example of a lid welding machine.
Sealing-related Failure Mechanisms:
Package Cracking; Soft Errors;
Pits and Voids; Incomplete Weld
A Sealing Furnace
A Lid Welding Machine
Manufacturing; Assembly Equipment
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