This page contains a Flash digital edition of a book.
July, 2017 Shadow Moiré Measurement Techniques Continued from page 51

sample. Die tilt angle can be shown from die to die or substrate to multi- ple dice.

Measure multiple groups or lots

of samples as desired. Measurement time is two seconds per group/lot, regardless of sample quantity, along with load and unload time. Finally, use the reference and die surface files created to batch process all results together. Die tilt angle can be calculated from the data sets within the batch processing interface.

Case Study Preparation In this study, 60 samples were

measured in two single shadow moiré measurements. The samples were measured inside JEDEC trays, as received. The chips came in a 4 x 11 layout JEDEC tray. The samples themselves were already production- quality devices that likely received outgoing quality checks. The focus of this case study was more to validate the concept and throughput of the solution.

Gauge results from the 60 sam-

ples were collected and considered these variables: height of the die from the substrate using a newly proposed technique to predict this height, given an initial estimate; die tilt angle with and without compen- sation for die warpage; and through- put time per batch/JEDEC tray. Traditionally, shadow moiré is

not used to measure surfaces with sudden changes in height. To under- stand this limitation and to find ways to circumvent it, we must look more closely at the shadow moiré phase stepping algorithm. The first step in a shadow moiré measure- ment is to determine the height associated with a single fringe peri- od, the fringe value. In practice, the fringe value is

calculated by comparison with a known step height calibration block, to make it more accurate. With a known height per fringe, the “phase” of each single pixel can be deter- mined by extracting the grayscale intensity value from each image, called intensity images, taken dur- ing the phase stepping process. A four-step phase stepping is used in this case. The sample and grating are moved apart the distance of the fringe value divided by four between each image, representing a 90° shift in the periodic fringe pattern. To this point, none of the calcu-

lations are limited by step heights. Thus, even across sudden step heights, the phase term is still valid. It is this concept that is critical to the new approach to measuring dis- continuing step heights, given an initial height estimate. The final equation converting

phase data to z-height information is where step heights pose a problem. Because phase occurs in a periodic manner, in order to translate phase data to z height, a counter integer must be tracked whenever a new phase begins. In order to determine a correct fringe order, a steady change in height is required.

A New Strategy A new strategy is proposed to

use an approximate height value input from the user and then use the available portion of the shadow moiré equation to determine a more accu- rate z height. This approach was test-


3001 Stafford Drive. Charlotte, NC. 28208 Ph: 704-394-0314

Incorrect shadow moiré processing of phase image. TAKAYA The Flying Probe Experts TAKAYA set a NEW standard in high performance and overall test

coverage with the introduction of its Advanced Multi-Function Flying Probe Systems, the APT-1400F and the NEW APT-1400F-SL

Unprecedented Test Speed and Accuracy at the Probe Tip Architecture provides fastest and most controlled probe movement

6 Topside Flying Probes Provide Optimum Access Flexibility Four angled probes, two vertical probes (no angle)

LED Color Test Option Allows functional testing of LED “Color & Luminance”

New TOS-7F Color Camera & Vision system for AOI New high intensity dual LED light ring provides direct camera lighting

Standard Intergrated Functional Test Capability Newly designed high measurement unit Integrated 4 quadrant power supplies Frequency Measurement Capability

Programmable Function generator - Sine wave, Square wave, etc.

APT-1400F / APT-1400F-SL Multi-function Flying Probe Systems

ed on the same samples as the die tilt case study. To look more closely at the numbers involved with the prediction of height and measurement accuracy, the initial height prediction must be within the fringe value divided by 2, and the accuracy for the shadow moiré measurement is fringe value divided by 100. In this case a 100 line per inch (LPI) grating is used so actu- al values translate to a required pre- diction accuracy of 127 µm and a final z-height accuracy of 2.5 µm. Using digital fringe projection

(DFP), the step height of the sample studied is first determined to be used as our prediction. DFP is capable of measuring surface step heights, but has worse accuracy, a smaller field of

Continued on page 57

Page 55



Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92