LENS CAP FOR A TRANSISTOR OUTLINE PACKAGE

Abstract

A lens cap for a transistor outline (TO) package is provided that has an inner diameter of less than 4 mm. The lens cap includes a metal shell with a wall thickness of less than 0.2 mm and a thinned area surrounding the lens so that in the thinned area the wall thickness is reduced by at least 35%.

Claims

1. A lens cap for a transistor outline package, comprising: a metal shell having a base wall, the metal shell having an inner diameter of less than 4 mm and a wall thickness of less than 0.2 mm at least at the base wall; an opening in the base wall, wherein the base wall includes a thinned area surrounding the opening, the thinned area having a wall thickness that is reduced by at least 35%; and a lens seated in the opening.

2. The lens cap as claimed in claim 1, wherein the wall thickness of the thinned area is reduced by at least 40%.

3. The lens cap as claimed in claim 1, wherein the wall thickness of the thinned area is reduced by at least 45%.

4. The lens cap as claimed in claim 1, wherein the thinned area is an impression in a deep drawn component.

5. The lens cap as claimed in claim 1, wherein the thinned area is a groove extending around the lens.

6. The lens cap as claimed in claim 1, wherein the thinned area is a flattening of the base wall extending around the lens.

7. The lens cap as claimed in claim 1, wherein the lens has an outer diameter between 1 and 2 mm.

8. The lens cap as claimed in claim 1, wherein the metal shell is made of a material exhibiting a coefficient of linear thermal expansion that differs by not more than 1 ppm/K from a coefficient of linear thermal expansion of the lens.

9. The lens cap as claimed in claim 1, wherein the lens is fused to the base wall of the metal shell.

10. The lens cap as claimed in claim 1, wherein the metal shell has a collar for securement of the lens cap to a header of the transistor outline package, and wherein the lens has a lens stem that is seated in the opening.

11. The lens cap as claimed in claim 1, wherein the transistor outline package is embodied as a TO-33 package.

12. The lens cap as claimed in claim 1, wherein the lens is made of borosilicate glass.

13. The lens cap as claimed in claim 1, wherein the metal shell is made of an iron-nickel alloy.

14. The lens cap as claimed in claim 1, wherein the metal shell has a shell wall thickness of less than 0.15 mm.

15. The lens cap as claimed in claim 1, wherein the opening has a diameter that is 40 to 60% of an outer diameter of the metal shell.

16. A transistor outline package comprising the lens cap as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The subject matter of the invention will now be explained in more detail by way of two exemplary embodiments with reference to the drawings of FIGS. 1 to 4.

[0044] FIG. 1 shows a perspective view of a first exemplary embodiment of a lens cap.

[0045] FIG. 2 is an axial sectional view of FIG. 1.

[0046] FIG. 3 shows a perspective view of an alternative embodiment of a lens cap.

[0047] FIG. 4 is again a sectional view of FIG. 3.

DETAILED DESCRIPTION

[0048] FIG. 1 is a perspective view illustrating a lens cap 1 according to a first embodiment of the invention.

[0049] Lens cap 1 has a cup-shaped design and comprises a metal shell 2 of essentially circular cylindrical shape with a base wall 8 comprising a lens 5 arranged in the center thereof.

[0050] At a lower end, the metal shell 2 has a collar 4 via serves to secure the shell to the header of a TO package (not shown).

[0051] Metal shell 2 has an inner diameter and a height of less than 4 mm. A ratio of height to width of the shell is preferably between 7:3 and 3:7.

[0052] The wall thickness of the metal shell 2 is preferably less than 0.2 mm, more preferably less than 0.15 mm.

[0053] Already in this view it can be seen that an annular thinned area 3 in the form of a groove is provided around the lens 5, which serves to reduce stresses in the area of the lens 5, in particular in the area of lens edge 11.

[0054] FIG. 2 is a sectional view of FIG. 1.

[0055] It can be seen that the metal shell 2 has a reduced thickness in the region of thinned area 3.

[0056] Therefore, lens 5 is seated on a base 6 immediately adjoining the thinned area 3. In this exemplary embodiment, base 6 and lens 5 are designed so that the lens edge 11 is arranged directly adjacent to the thinned area 3.

[0057] Lens 5 has been fused into the opening 10 and comprises a lens stem 7 extending into the opening 10 of metal shell 2. Lens stem 7 merges into a larger diameter section 12 and into a smaller diameter section 13 disposed inside the lens cap.

[0058] Base 6 preferably has a width b of at least 0.1 mm, more preferably at least 0.15 mm.

[0059] The corner 9 of metal shell 2 is preferably rounded.

[0060] It has been found that the mechanical stability of the lens cap 1 can be considerably increased already with a rather narrow thinned area 3.

[0061] What is decisive for the mechanical stability of lens cap 1 is the depth of the thinned area 3. The wall thickness in the thinned area should be reduced by at least 35%, preferably at least 40%, compared to the adjacent wall of base 6 and/or the adjacent non-thinned region of metal shell 2.

[0062] FIG. 3 shows a perspective view of an alternative embodiment of the invention in which the entire base wall 8 of the metal shell around lens 5 is thinned, in contrast to the embodiment illustrated in FIGS. 1 and 2.

[0063] FIG. 4 is a sectional view of FIG. 3.

[0064] It can be seen that the lens 5 is again seated on a base 6 in this embodiment.

[0065] Lens 5, or the upper section of the lens thus sits on a circular base 6 around which the material of metal shell 2 includes a thinned area 3 and is thinned as far as to the corner 9 in this embodiment.

[0066] This shell also has a diameter d.sub.i and a height h of less than 4 mm.

[0067] The outer diameter d.sub.A is defined as the outer diameter of the metal shell 2 above collar 4 which serves to secure the metal shell 2 to the header of a TO package.

[0068] The invention permits to provide even small lens caps of good mechanical stability.

LIST OF REFERENCE NUMERALS

[0069] 1 Lens cap [0070] 2 Metal shell [0071] 3 Thinned area [0072] 4 Collar [0073] 5 Lens [0074] 6 Base [0075] 7 Lens stem [0076] 8 Base wall [0077] 9 Corner [0078] 10 Opening [0079] 11 Edge of lens [0080] 12 Larger diameter portion [0081] 13 Smaller diameter portion