Plastic electronic component package
A plastic package for an image sensor or other electronic component which comprises a plastic body, preferably of LCP material, molded around a leadframe and defining a cavity in which the image sensor is to be disposed. A lid assembly is provided having a transparent glass lid retained in a plastic lid frame which is weldable or otherwise bondable to the plastic body of the package to enclose the image sensor mounted in the cavity. The leadframe is usually composed of copper or a copper alloy, or a ferrous alloy having a copper coating. An interfacial layer is formed on the surfaces of the leadframe at least in those portions which are in contact with the plastic body which serves to provide substantially improved adhesion between the leadframe and the plastic material to achieve a hermetic bond between the metal and plastic materials. The interfacial layer is composed of a cuprous oxide base layer formed on a surface of the leadframe, and a cupric oxide layer formed on the cuprous oxide layer. The cupric oxide outer layer has an acicular structure which provides an interlocking mechanism for adhesion to the plastic material molded thereto in forming the package.
1. A method of forming a hermetic seal between a metal element and a high temperature plastic element, the method comprising the steps of:
oxidizing a surface of the metal element by reacting the surface with a chemical oxidizer solution at a temperature of about 212-216° F. for greater than 10 minutes, whereby a first oxide layer consisting essentially of cuprous oxide is formed on the metal surface, and whereby substantially simultaneously a second oxide layer consisting essentially of cupric oxide with an acicular structure is formed on the first oxide layer; and
applying a high temperature plastic material onto the second oxide layer to form the plastic element.
2. The method of claim 1 , wherein the metal element has a copper surface at least in the area bondable to the plastic element.
3. The method of claim 1 , wherein the metal element consists essentially of copper or a copper alloy.
4. The method of claim 1 , wherein the high temperature plastic material is a liquid crystal polymer (LCP) material.
5. The method of claim 4 , wherein the LCP material is a polymer formed from one or more monomeric units selected from the group consisting of hydroquinone, terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxyclic acid, 4-hydroxybenzoic acid, bisphenol, and hydroxynaphthoic acid.
6. The method of claim 1 , wherein the plastic material comprises one or more types of filler particles selected from the group consisting of talc, glass fiber, milled glass, and flake glass.
7. The method of claim 6 , wherein the filler particles are in the range of 10-50% by weight of the plastic material.
8. The method of claim 6 , wherein at least some of the filler particles, have a particle size in the range of about 50-350 microns.
9. The method of claim 6 , wherein at least some of the filler particles are of nano size.
10. The method of claim 1 , wherein the first and second oxide layers are applied to a portion of the surface of the metal element.
11. The method of claim 1 , wherein the first and second oxide layers are applied to the entire surface of the metal element.
12. The method of claim 1 , further comprising the step of removing the exposed portions of the first and second oxide layers from the metal element after applying the plastic material.
13. The method of claim 1 , wherein the plastic material is applied by a molding process.
14. The method of claim 13 , wherein the molding process comprises injection molding.
15. The method of claim 1 , wherein the step of oxidizing is performed by reacting with the chemical oxidizer solution for about 20 minutes.
16. The method of claim 1 , wherein the LCP material has a melting temperature greater than about 300° C.
17. The method of claim 1 , wherein the plastic material has a coefficient of thermal expansion (CTE) compatible with that of the metal element.
18. The method of claim 17 , wherein the CTE of the plastic material is in the range of about 6-25 ppm/° C.
19. The method of claim 1 , wherein the chemical oxidizer solution is an alkaline solution.
20. The method of claim 1 , wherein the first oxide layer and the second oxide layer together have a thickness of about 1-10 microns.
21. The method of claim 1 , wherein the seal withstands a dye gross leak test according to standard MIL-STD-883, Test Condition D.