Compact Ringlight

Abstract

A compact ringlight that emulates the performance of a much larger ringlight is disclosed. The invention utilizes a ringlight source and a conical or cylindrical reflector such that light first crosses the optical axis and then is reflected back towards the inspection area. This light is particularly useful for inspecting electronic semiconductor devices.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of prior art.

FIG. 2 is a side section view of prior art utilizing a standard LED ringlight and camera to inspect a BGA device.

FIG. 3 is a depiction of a camera image of the prior art depicted in FIG. 1.

FIG. 4 is an isometric view of the invention.

FIG. 5 is a cutaway isometric view of the invention.

FIG. 6 is a side section view of the invention and a BGA device.

FIG. 7 is a cutaway isometric view of another embodiment of the invention.

FIG. 8 is a cutaway side view the FIG. 7 embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Turning now descriptively to the drawings, in which similar reference characters denote similar elements throughout the several views, the attached figures illustrate the compact ringlight.

FIG. 4 illustrates a preferred embodiment of the invention. A circular array of LEDs 1 is attached to a circuit board 2. The LEDs are positioned to emit light inward toward the ringlight's axis of symmetry 26 which is also the optical axis of the system. A conical reflective surface 11 is formed by the inner surface of a piece of metal 12. A ring 13 forms an aperture so that light from the LEDs cannot directly illuminate the inspection area but must cross above the inspection area (passing thru the optical axis of the system) and be reflected off of the reflective surface on the opposite side before illuminating the inspection area. A light shaping diffuser 25 (FIG. 5) radially diffuses light.

FIG. 6 is a cut-away side view of the invention positioned above BGA device 30. LED 14 produces a broad diverging beam of light, the outermost rays are depicted as rays 15 and 16. Ray 15, however, is blocked by the ring aperture as are any other rays that could otherwise directly illuminate the inspection area. Ray 16 passes out of the system. Ray 17 just barely clears the ring aperture and passes across the optical axis and above device 4 to be incident on reflective surface 11. The reflected ray 19 is directed back towards the inspection area.

Ray 18 produced by LED 14 passes across the optical axis and above device 4 to be reflected off of reflecting surface 11 as ray 20 which is also directed back towards the inspection area. Any rays produced by LED 14 that are above ray 18 will not be incident on reflecting surface 11 and will not contribute to lighting the inspection area. The result is that only light that has reflected off of reflecting surface 11 will be incident on the device in the inspection area. Therefore the light has traveled approximately 1½ times the diameter of the ringlight before illuminating the device. This long distance means that the vertical angle of incidence of the light across the inspection area is nearly constant (nearly collimated). The long distance also decreases the variation of light intensity across the inspection area.

Another preferred embodiment is illustrated in FIG. 7's cutaway isometric view. To avoid bending the LEDs, an additional reflecting surface has been used to create the ringlight. In this case the LEDs 21 are perpendicular to the printed circuit board 22 and aim down to a reflecting surface 23 that is integrated into a piece of metal 24 that also contains the conical reflecting surface 11. Reflecting surface 23 redirects the LED light to travel along the same path as in the previous embodiment. FIG. 8 shows a cutaway side view of this embodiment.

The preferred embodiments use LEDs, 1 however other light sources such as filament or gas bulbs or lasers could be used. A circle of fiber optics could also be used.

The conical reflective surface 11 of the embodiments discussed is formed on metal such as aluminum. Other materials could be used so long as they reflect light sufficiently. Reflective coatings could be used as well. Also the shape need not be conical to embody the idea of the invention. A cylindrical shape could be used. An octagonal or other polygonal shape could also provide the reflective surface required to embody the invention. A paraboloidal shape can collimate the light even further.

The ring aperture 13 is black to absorb light however it could be other colors and the aperture would still function. It is made of metal, however plastic and various other materials would suffice. Alternatively the aperture could be replaced with microlouvers or a lens or other optical baffle so long as light is substantially blocked from illuminating the inspection area directly without first crossing the optical axis and reflecting off of the reflective surface. Alternatively the light source could produce a narrow beam profile where no aperture is required such as with lasers. It should be mentioned that not all desired rays precisely intersect the optical axis, but rather generally pass by the optical axis prior to being incident on the reflective surface.

The light shaping diffuser 25 is a lenticular diffuser consisting of an array of vertically oriented cylindrical lenses to spread light radially (laterally). The diffuser could be some other engineered refractive diffuser such as an array of small lenslets, or standard diffuser material, or holographic diffuser or some other means of diffusion. Spreading light laterally causes the light from all directions to more equally contribute to illuminating each portion of the inspection area. For example, when illuminating BGA balls, balls that are in the corner of the inspection area have circles that are of more even intensity all the way around because of the diffuser. This diffuser also eliminates varied intensity patterns in the inspection area due to the lateral focusing caused by the conical reflector. Alternatively, this diffuser could be eliminated by integrating lateral diffusion into one of the conical reflecting surfaces (23 or 24 of FIG. 7) such as by adding vertical grooves.

Claims

1. A compact ringlight that emulates the performance of a larger ringlight, said compact ringlight comprising: a) an annular light source that emits light inward towards its axis of symmetry,b) a reflector which has an annular inner reflecting surface,c) positioning said annular light source and said reflector such that their axis of symmetry is substantially coincident and such that light from said light source substantially passes through the axis of symmetry prior to being incident on said reflector which then directs the light towards an inspection area.

2. The compact ringlight of claim 1 which additionally comprises a diffuser to radially diffuse light prior to passing through the axis of symmetry.

3. The compact ringlight of claim 1 which additionally comprises a baffle that blocks light from directly illuminating the inspection area without first reflecting off of the annular reflector.

4. The compact ringlight of claim 1 wherein said annular reflecting surface is conical.

5. The compact ringlight of claim 1 wherein said annular reflecting surface is cylindrical.

6. The compact ringlight of claim 1 wherein said annular reflecting surface is polygonal.

7. The compact ringlight of claim 1 wherein said annular light source additionally comprises an annular reflector used to aim light towards said axis of symmetry.

8. A method for illuminating an object with darkfield lighting, said method comprising: a) emitting light from a ring and towards the axis of symmetry of said ring,b) positioning an annular reflective surface such that its axis of symmetry is substantially coincident with the axis of symmetry of said ring, and such that light from said ring is incident on said annular reflective surface after passing through the axis of symmetry of said ring,c) inhibiting said light from directly striking said object without first reflecting on said annular reflective surface.

9. The method of claim 8 which additionally comprises radially diffusing said light.

10. The method of claim 8 wherein said annular reflective surface is conical in shape.

11. An apparatus for inspecting an electronic semiconductor device with darkfield lighting, said apparatus comprising: a) a ringlight that emits light towards a center point located on the axis of symmetry of said ringlight,b) an electronic camera positioned so that its optical axis is substantially coincident with the axis of symmetry of said ringlight,c) a reflector which has an annular inner reflecting surface,d) positioning said reflector such that its axis of symmetry is coincident with the axis of symmetry of said ringlight and such that after light from the ringlight passes through said axis it is incident on said reflector which then reflects the light towards said electronic semiconductor device,e) optical means for preventing light from said ringlight from directly illuminating said electronic semiconductor device without first reflecting off of said reflector.

12. The apparatus of claim 11 which additionally comprises a diffuser to diffuse light radially with respect to said axis of symmetry.

13. The apparatus of claim 11 which additionally comprises a baffle that blocks light from directly illuminating the inspection area without first reflecting off of the conical reflector.

14. The apparatus of claim 11 which additionally comprises a flat plate with a circular aperture, said plate positioned to block light from directly illuminating the inspection area without first reflecting off of the conical reflector.

15. The apparatus of claim 11 wherein said ringlight of claim 1 wherein said annular inner reflecting surface is substantially paraboloidal.