Advanced Packaging, X-Ray Inspection and the Humble LED

 In

by Keith Bryant, Global Sales Director, Electronics, Yxlon International

The excellent recent Microtech 2018 Conference, organized by IMAPS UK to celebrate the 50th anniversary of their founding, had very strong papers reflecting the developments of advanced electronic packaging over the last 50 years and the drivers and needs for advanced packaging’s future. In other words, ‘where have we been and where are we going?’. In this regard, as advanced packaging continues to develop to support novel and emerging technologies, the need for, non-destructive, test and inspection continues to be vital to ensure the quality and assurance of their functionality, be it simple or complex in nature, wherever, and in whatever harsh environment, the package may end up. This is made ever more difficult as package complexity increases, whilst the feature sizes within continue to decrease. X-ray technology has long been an important part of the non-destructive inspection protocol over the history of advanced packaging and will continue to play an ever more important part in the future. The advances made in both 2D and 3D X-ray inspection over recent years and the new opportunities that are now starting to be available, especially within 3D, or CT, inspection, will enable our 120-year-old X-ray technology to remain relevant to, and be supportive of, the future needs of advanced packaging. 

To highlight where X-ray inspection has, can and will support the needs of advanced packaging applications, an obvious case study would be to consider the humble LED. LEDs are a great example of the remarkable developments in packaging and technology over the last 20 years, let alone the last 50. Their need to use higher power, produce better light, contain ever shrinking features and customer demand for increased reliability for expanding manufacturing volumes, intensify the need, today and tomorrow, for higher quality, more consistent production output. Flaws cannot be accepted, especially as higher operating powers typically mean higher package operating temperatures which, in turn, then requires very good thermal conductivity and heat transfer within the package to move heat away from key areas. Without good heat dissipation then heat stresses at the interfaces can cause delamination or die fractures, leading to early product failure and / or reducing LED lifetimes. The presence of voids, particularly at the die to package interface, create air gaps that reduce heat transfer efficiency. As many LEDs are potted, or encapsulated, the only non-destructive test option to check for voiding, and other faults that are shown below, is by using 2D and CT X-ray analysis. Without implementing suitable test and inspection procedures, such failures may be only an inconvenience when an LED is within a home light bulb, but it may be much more serious when the device is located within an automotive application. The automotive industry’s necessary, long-established, and well-known focus on product quality, especially for safety critical applications, is well known, as is their extremely tight manufacturing quality demands on their suppliers. 

X-ray Developments

The developments in X-ray technology over the last 20 years that have resonance for LED and other advanced packaging applications include the following:

Better transmission-style X-ray tubes, giving high magnification capabilities that is necessary for inspecting the tiny features within LEDs.

Improved X-ray tube resolution, providing better clarity in the 2D X-ray images to enable better analysis of smaller features.

The ability to image at oblique angle views without losing the available magnification, else analysis of the small joint interfaces is likely to be obscured by the bulk of the joint.

The use of 3D X-ray, or CT, techniques to provide ultimate failure analysis by being able to take ‘virtual 2D X-ray micro-sections’ through any plane of a sample as well as produce and manipulate 3D rendered visualisations.

The availability and relatively low cost of incredible computing power in GPUs that are located within high end imaging cards developed for gaming applications on fast home PCs. These permit much quicker CT reconstructions and CT volume manipulation as well as provide the opportunity for new, and better, CT reconstruction algorithms to be used. An example of this is the use of helical CT scanning to produce the CT model as an alternative to the cone beam, or FDK, CT algorithm.

The emergence of the Partial CT (PCT), or limited angle CT, X-ray technique where 3D analysis can be achieved at higher magnification fields of view on much larger samples than can be achieved in ‘full’ CT.

Flaws in LEDs

The earliest NIR LEDs were commercially available in the 1960s. Thereafter, LED development concentrated on moving towards producing light at shorter wavelengths. However, it was not until the late 1990s, when high power blue LEDs became commercially available, that it could be said that today’s ubiquity of the LED started. Without the blue/UV light, it is not possible to produce white light. White light can be produced, either through the blending of red, green and blue light (RGB method), as found in an LED TV, or using the phosphor method where blue/UV light excites a yellow phosphor, as found in high brightness LEDs used for illumination. 

Although LEDs are relatively simple devices and single LEDs have a low individual cost, failures can still occur which, if not corrected during production can cause substantial wastage and yield loss. Image 1 shows X-ray images of two different single-LEDs. On the left is an example of what we would expect 

X-ray Developments

The developments in X-ray technology over the last 20 years that have resonance for LED and other advanced packaging applications include the following:

Better transmission-style X-ray tubes, giving high magnification capabilities that is necessary for inspecting the tiny features within LEDs.

Improved X-ray tube resolution, providing better clarity in the 2D X-ray images to enable better analysis of smaller features.

The ability to image at oblique angle views without losing the available magnification, else analysis of the small joint interfaces is likely to be obscured by the bulk of the joint.

The use of 3D X-ray, or CT, techniques to provide ultimate failure analysis by being able to take ‘virtual 2D X-ray micro-sections’ through any plane of a sample as well as produce and manipulate 3D rendered visualisations.

The availability and relatively low cost of incredible computing power in GPUs that are located within high end imaging cards developed for gaming applications on fast home PCs. These permit much quicker CT reconstructions and CT volume manipulation as well as provide the opportunity for new, and better, CT reconstruction algorithms to be used. An example of this is the use of helical CT scanning to produce the CT model as an alternative to the cone beam, or FDK, CT algorithm.

The emergence of the Partial CT (PCT), or limited angle CT, X-ray technique where 3D analysis can be achieved at higher magnification fields of view on much larger samples than can be achieved in ‘full’ CT.

Flaws in LEDs

The earliest NIR LEDs were commercially available in the 1960s. Thereafter, LED development concentrated on moving towards producing light at shorter wavelengths. However, it was not until the late 1990s, when high power blue LEDs became commercially available, that it could be said that today’s ubiquity of the LED started. Without the blue/UV light, it is not possible to produce white light. White light can be produced, either through the blending of red, green and blue light (RGB method), as found in an LED TV, or using the phosphor method where blue/UV light excites a yellow phosphor, as found in high brightness LEDs used for illumination. 

Although LEDs are relatively simple devices and single LEDs have a low individual cost, failures can still occur which, if not corrected during production can cause substantial wastage and yield loss. Image 1 shows X-ray images of two different single-LEDs. On the left is an example of what we would expect 

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