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October, 2017
The Economics of Die Attach Voiding in LED Assemblies
I
mprovements in high-brightness LED technologies are making these devices useful for general illumination. But, before LEDs can completely replace outmoded light sources, their thermal management schemes need to be further developed to ensure consistent color quality and long operational lifetimes. In partic- ular, the bonding technologies that hold the LED components together need to be improved. Localized heat generation is
By Griffin Lemaster, Dr. Bill Cardoso and Dr. Glen Thomas, Creative Electron, Inc. To better illustrate the econom-
ics of LED die attach voiding, Creative Electron analyzed a real-life scenario.
ranty options to its customers: a standard 38,000-hour warranty, which is free, or an extended 50,000- hour warranty at extra cost. It is
l l
l Price of a single luminaire: $100. l
Price of 50,000-hour extended warranty: $20.
Production and distribution costs: $35.
Warranty cost: $5. This pricing model is based on
caused by the semiconductors in these devices. For maximum lumen output, color consistency and device lifetime, this heat must be dissipated efficient- ly, allowing the LED junction temper-
ature (TJ) to remain stable. The rate at which an LED mod-
ule ages is highly dependent on the temperature at the p-n junction and will accelerate over time. As a result, service life values are only valid pro- vided that certain p-n junction tem-
peratures (Tj) are not exceeded. The values are determined statistically during test runs undertaken by LED manufacturers and do not reflect the precise behavior of individual LEDs. The same applies to LED
brightness values. The heat generat- ed at the p-n junction impairs the efficiency of the light generation and results in a measurable drop in brightness.
Clockwise from top left: photo of LED assembled on substrate; X-ray inspection image of LED; X-ray inspection image with identified and measured voids using TruView software; and 3D rendering of die-attach voids.
One of Creative Electron’s cus-
tomers is a large contract manufac- turing company new to the LED luminaire market. It offers two war-
MID AMERICA Taping and Reeling, Inc.
630.629.6646
www.matr.com
understood that a single LED failure results in a luminaire fail. For this analysis we assume the following pricing model:
the expectation that within the stan- dard warranty period the company will receive up to 5 percent in returns, and up to 20 percent within the extended warranty period. The LED manufacturer wanted
to better understand if the amount allocated to warranty costs was enough. It could fabricate LED lumi- naires with a reasonable profit mar- gin, but feared that these margins would be destroyed by returns of product under warranty.
Void Area and Operating Temperature To determine the operating tem-
perature of an LED mounted on a substrate, we first calculate the ther- mal resistance between the LED and the substrate. This thermal resist- ance, (R), is given by:
where x is the thickness of the die attach, k is the thermal conductivity
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