Chun-Sam Song

Detection of Flip-chip Bonding Error Through Edge Size Extraction of X-ray Image

The technology to inspect and measure an inner structure of micro parts has become an important tool in the semi-conductor industrial field with the development of automation and precision manufacturing. Especially, the inspection skill on the inside of highly integrated electronic device becomes a key role in detecting defects of a completely assembled product. X-ray inspection technology has been focused as a main method to inspect the inside structure. However, there has been insufficient research done on the customized inspection technology for the flip-chip assembly due to the interior connecting part of flip chip which connects the die and PCB electrically through balls positioned on the die. In this study, therefore, it is implemented to detect shape error of flip chip bonding without damaging chips using an x-ray inspection system. At this time, it is able to monitor the solder bump shape by introducing an edge-extracting algorithm (exponential approximation function) according to the attenuating characteristic and detect shape error compared with CAD data. Additionally, the bonding error of solder bumps is automatically detectable by acquiring numerical size information at the extracted solder bump edges.

Analysis of the laser transmission rate of silicon (Si) applied to flip-chip bonding

The present study explored a flip-chip packaging method where transmission bonding is performed using the laser beam transmission rate of Si, the main material of flip chips. Here, the transmission of Si by a laser beam using laser wavelength in the IR domain (1,064 nm) was demonstrated through experiments. Further experiments were then conducted where the results were applied to actual flip chip bonding. The mechanical properties of the flip-chip solder joints were analyzed through experiments, and the degree of thermal effect was analyzed through simulation. The results showed that, in flip chip bonding, laser transmission bonding was advantageous in mechanical, thermal, and temporal terms relative to conventional bonding (thermo-compression).

Development of 3-D shapes estimation by using single X-ray image

X-ray images are heavily affected by noise which makes normal image processing not workable. This paper suggested a new method to identify the primary 3-D shape of an embedded object and its pose by using only single X-ray image. The image feature consists of corner points and edge/intersection lines of adjacent surfaces. The intensity of an X-ray image is attenuated exponentially with increasing the penetration thickness. The main finding is to model a precise exponential relationship to fit the variation of X-ray image intensity. It applied a least-square-method to the X-ray projection image and effectively extracted edges and intersection lines from the noise of X-ray image.

A Study on the Optimization of IR Laser Flip-chip Bonding Process Using Taguchi Methods

A flip-chip bonding system using IR laser with a wavelength of 1064 nm was developed and associated process parameters were analyzed using Taguchi methods. An infrared laser beam is designed to transmit through a silicon chip and used for transferring laser energy directly to micro-bumps. This process has several advantages: minimized heat affect zone, fast bonding and good reliability in the microchip bonding interface. Approximately 50 % of the irradiated energy can be directly used for bonding the solder bumps with a few seconds of bonding time. A flip-chip with 120 solder bumps was used for this experiment and the composition of the solder bump was Sn3.0Ag0.5Cu. The main processing parameters for IR laser flip-chip bonding were laser power, scanning speed, a spot size and UBM thickness. Taguchi methods were applied for optimizing these four main processing parameters. The optimized bump shape and its shear force were modeled and the experimental results were compared with them. The analysis results indicate that the bump shape and its shear force are dominantly influenced by laser power and scanning speed over a laser spot size. In addition, various effects of processing parameters for IR laser flip-chip bonding are presented and discussed.

Study of a Low-Temperature Bonding Process for a Next-Generation Flexible Display Module Using Transverse Ultrasound

This is direct bonding many of the metal bumps between FPCB and HPCB substrate. By using an ultrasonic horn mounted on an ultrasonic bonding machine, it is possible to bond gold pads onto the FPCB and HPCB at room temperature without an adhesive like ACA or NCA and high heat and solder. This ultrasonic bonding technology minimizes damage to the material. The process conditions evaluated for obtaining a greater bonding strength than 0.6 kgf, which is commercially required, were 40 kHz of frequency; 0.6MPa of bonding pressure; and 0.5, 1.0, 1.5, and 2.0 s of bonding time. The peel off test was performed for evaluating bonding strength, which was found to be more than 0.80 kgf.

A Study on 3-D Information Extraction using Single X-ray Image

이차원 및 3차원 형상 및 치수 측정 기술은 자동화 및 정밀 생산 기술의 발전과 함께 산업 현장에서 요구되는 중요한 기술이 되었다. 특히, 최근 반도체 산업의 발달로 인하여 전자기기가 점차 소형화 되고, 생산이 자동화됨에 따라 각종 전자 부품들에 대한 정밀한 검사가 중요한 문제로 대두되었으며, 이에 따라 레이저 및 시각 검사 및 측정 기술이 연구되어 왔다. 특히, 고집적 화된 전자기기의 내부 구조에 대한 검사는 조립이 완료된 제품의 결함 판정에 있어서 중요한 역할을 하고 있다. 내부 구조에 대한 검사에선 내부 구조물의 형상 및 자세에 대한 기하학적인 정보가 필요하며, 이러한 내부 구조물에 대한 검사방법으로 X선 검사 방법의 연구가 진행 되고 있다. X선을 이용한 내부 구조물에 대한 자세 및 형상 측정에 관한 연구는 의료 분야에서 인체의 내부를 대상으로 한 연구가 주로 이루어졌다. 그 대표적인 예로 MRI, 토모그라피(Tomography)등과 같은 단층 촬영 기법을 들 수 있다. MRI는 여러 장의 X선 영상을 얻어 대상의 3차원 표면 모델링을 하고 영상 매칭에 이를 이용한다. 이 방법은 삼차원 표면 형상에 대한 모델을 사용하여 곡면의 형상을 갖는 물체에 적용한 것에 큰 의의가 있다. 그러나, 영상에서의 윤곽 정보만을 사용하는 방법이므로 가림에 대한 X선 영상의 장점을 충분히 활용하지 못하여, 외곽 점들의 매칭에 사용되는 일치점을 찾는 것이 어려운 문제이다. 토모그라피는 단면에 대한 영상을 얻기 위한 방법으로 구하고자 하는 단면 주위로 각 방향의 X선 투영 값을 얻어 연산에 의하여 단면에 대한 영상으로 재구성하는 방식이다. 토모그라피 영상법은 특정 단면 형상을 정확하게 구할 수 있는 방법으로 알려져 있으나 한 단면 영상을 구하기 위하여 많은 수의 영상을 촬영해야 한다는 문제점이 있다. 또한 단면에 대한 전 방향에서의 투과 영상이 요구되므로 대상에 따라 단면 영상 취득이 어려운 문제점을 갖는다. 따라서 산업적인 응용 면에서 X선 영상을 이용한 형상 및 자세 측정 연구 사례나 X선 영상으로부터 특징치를 구하기 위한 영상 처리 기법에 대한 연구가 미흡한 실정이다. 본 연구에서는 한 장의 X선 영상에서 대상 물체의 기하학적 정보를 얻어 낼 수 있는 영상 처리 기법에 관한 방법을 제시하였다.

Study of Metal(Au) Bump for Transverse Ultrasonic Bonding

In this paper, the direct bonding process between FPCB and HPCB was studied. By using an ultrasonic horn which is mounted on the ultrasonic bonding machine, it is alternatively possible to bond the gold pads attached on the FPCB and HPCB at room temperature without an adhesive like ACA or NCA. The process condition for obtaining more bonding strength than 0.6 Kgf, which is commercially required, was carried out as 40 kHz of frequency, 0.6 MPa of bonding pressure and 2 second of bonding time. The peel off test was performed for evaluating bonding strength which results in more than 0.8 Kgf.

Edge extraction in X-ray image based on COD of materials

We have performed a single X-ray image extract of three-dimensional shape information (edges and vertex) by using characteristics of a specific material with a specific size (thickness). We have used that fact that the intensity distribution X-ray images decreases around edge areas in the form of exponential function and used the least square method and the coefficient of determination value to extract edges. Here we could infer the effect of the penetration rate of X-ray on the coefficient of determination value according to the kind of material (Zn, Ti, A, and Si) and that the penetration rate and the coefficient of determination value are inversely proportional. We could also conclude the effect of the penetration rate of X-ray on the coefficient of determination value according to the size of the material (5, 10, 15mm) differs and the size and the coefficient of determination value are proportional.

Sensor system for linear defect tracking by using cone-shaped laser beam

A sensor system that measures the 3D data of the object after projecting the cone shaped beam to the object of measurement to create a round mark and receiving this image through camera, was studied. This sensor system, when attached to a robot, will enable diverse application works, and in this study, such was proved by displaying the tracking work for the defect fabricated randomly.

Detection of shape error through solder bump edge extraction of flip-chip by using exponential approximation function

As the technology of semi-conductor chip progresses to pursue high density and high speed, flip-chip technology recently has played a successful role to overcome technological limit of the existent gold wire bonding technology made a connection with outside terminal. Flip-chip is systemically different to the existent chip that transfers electrical signal by connecting wires to the chip externally. Because the interior connecting part of flip-chip is hidden into an invisible region between a die and a PCB, it is indispensable for preparing cut or sliced chips to observe inner joint parts. Therefore, this work embodied nondestructive inspection system that can examine the bonding part of flip-chip without damage of chip using an X-ray system. Using an attenuation characteristic of X-ray (the intensity after transmitting an X-ray), it could do monitoring the shape of solder bumps without damaging the chip. The suggested inspection method can effectively extract the edge of solder bumps from an X-ray image by using the exponential approximation for the intensity of transmitting an X-ray and detect inside bad bonding parts utilizing information about shape. The embodied inspection system is applied to evaluate actual bonded flip-chip.