Method for manufacturing a surface mount device
View Patent ↗A method of manufacturing a surface mount device includes providing at least one core device and at least one lead frame. The core device is attached to the lead frame. The core device and the lead frame are encapsulated within an encapsulant. The encapsulant comprises a liquid epoxy that when cured has an oxygen permeability of less than approximately 0.4 cm3·mm/m2·atm·day.
1. A surface mount device comprising:
a core device;
a contiguous, first conductive layer disposed on a first surface of the core device and a contiguous, second conductive layer disposed on a second surface of the core device opposite the first surface, the first conductive layer and the second conductive layer separate from one another;
a first conductive coating covering a first end of the core device and in direct contact with the first conductive layer and the second conductive layer;
a second conductive coating covering a second end of the core device opposite the first end and in direct contact with the first conductive layer and the second conductive layer, the second conductive coating separate from the first conductive coating;
an encapsulant surrounding at least a portion of the core device and the first and second conductive coatings, wherein the encapsulant corresponds to a cured version of a liquid epoxy and has an oxygen permeability of less than approximately 0.4 cm3·mm/m2·atm·day.
2. The surface mount device according to claim 1 , wherein the encapsulant corresponds to a thermoset epoxy.
3. The surface mount device according to claim 2 , wherein prior to curing, the epoxy has a viscosity of between about 1500 cps and 3000 cps.
4. The surface mount device according to claim 2 , wherein the epoxy comprises between about 10% to 50% filler content by weight.
5. The surface mount device according to claim 1 , wherein at least one of the first and second conductive coatings is formed of a conductive epoxy.
6. The surface mount device according to claim 1 , wherein the core device is a positive-temperature-coefficient (PTC) device.
7. The surface mount device according to claim 1 , wherein the encapsulant is applied via a transfer molding system.
8. The surface mount device according to claim 7 , wherein prior to curing, the encapsulant is inserted into a pot of the transfer molding system and heated to a temperature of between about 20° C.-30° C. and a pressure of between about 150 psi and 300 psi is applied to the encapsulant to force the encapsulant through a sprue of the molding system and around the portion of the core device.