CN201844818U - BGA (ball grid array) coplanarity measurement system based on projection Moire principle - Google Patents

Abstract

The utility model discloses a BGA coplanarity measurement system based on the principle of projection moiré, which comprises a cold light source (1), a collimator lens (3), a CCD camera (2, 4), an LCD panel (5), and a projection lens (6), an optical platform (7), a high-precision mobile station (8) and a computer (9). The stripe pattern generated by the computer (9) is displayed on the LCD panel (5), and the light emitted by the cold light source (1) is irradiated on the described LCD panel (5) after the collimating lens (3), and the display The fringe pattern on the LCD panel (5) is projected onto the reference plane or the surface of the object to be measured loaded on the high-precision mobile platform (8), and the CCD cameras are two, symmetrically arranged on the LCD panel (5 ) on both sides. The measurement area and measurement accuracy of the utility model are greatly improved, and can meet the requirements of large-area, high-precision, real-time and rapid measurement required in today's packaging and testing.

Description

A BGA Coplanarity Measuring System Based on Projection Mohr Principle

technical field

The utility model belongs to the field of electronic packaging, in particular to a measuring system for coplanarity of packaging devices in electronic packaging. It is suitable for real-time detection of the coplanarity of large-scale integrated circuit packages such as BGA (Ball Grid Array) and CSP (Chip Size Package).

Background technique

The integrated circuit (IC) industry has become the key to the development of the national economy, and IC design, manufacturing and packaging testing are the three pillars of the IC industry development. In actual production, due to the lack of on-line and off-line evaluation methods, many products fail to discover hidden dangers in the reliability of the products before they are put into the market, and even can only detect their processing quality and reliability through the use process of the device, which seriously hinders micro The rapid development of the electronics industry. Today, with the continuous emergence of various new packaging materials, structures and processes, IC packaging and testing is particularly important. Because the packaging test can detect the morphology characteristics of the device during the packaging process in real time, and can also detect the quality of each packaged device, and quickly find defective products in mass production. It provides guarantee for the consistency, repeatability, reliability and durability of IC products.

Ball grid array (Ball-Grid-Array) is the most popular packaging technology today. In the process of BGA packaging, the warping of the substrate caused by factors such as the mismatch of the thermal expansion coefficient (CTE) of the material and the unevenness of the BGA solder ball itself will lead to the non-coplanar situation of the BGA solder balls on the substrate, which will induce circuit failure. Short circuit or open circuit leads to unsafe electrical connection, affects electrical connection performance and product reliability, and even causes device failure. Therefore, the coplanarity inspection of BGA solder balls is crucial.

Today, the three-dimensional testing system for BGA solder ball coplanarity inspection is mainly based on laser scanning technology or structured light projection method. The physical scanning process of the laser beam results in very low measurement speeds. Moreover, the traditional detection method is to move the position of the reference grid through mechanical movement to achieve phase shift. The moving speed is slow, and the movement brings vibration, noise, and poor repeating phase shift accuracy, which cannot meet the requirements of high-precision real-time measurement. At the same time, there are two difficulties in applying the structured light projection method to the coplanarity detection: 1. The size of the chip to be tested is small, which requires a high resolution of the measurement system. 2. There is specular reflection on the surface of the chip, and the chip substrate is generally a dark material, and the contrast of the light projected onto the two surfaces is poor. As the measurement area increases, the measurement range of the device under test increases in the depth direction, and the requirements for measurement accuracy and efficiency continue to increase, a stable and reliable fast measurement method is urgently needed.

Contents of the invention

The purpose of this utility model is to propose a BGA coplanarity measurement system based on projection moiré, which combines projection moiré and LCD phase shift technology, adopts an incoherent cold light source and an LCD virtual grating to vertically project sinusoidal stripes The pattern is projected onto the surface of the object to be measured or the reference plane under the field of view of the CCD camera, and the cold light source is used to project vertically onto the reference plane and the double-sided CCD tilting imaging mechanism solves the problem that the part of the shadow area caused by the single-sided CCD camera cannot be captured. It can also eliminate the influence of specular reflection, ensure the uniformity of the projection intensity of the entire light field, and provide more moiré fringe information, which improves the measurement accuracy.

The technical scheme adopted for realizing the purpose of this utility model is:

A BGA coplanarity measurement system based on the projection Moiré principle, comprising a cold light source, a collimator lens, a CCD camera, an LCD panel, a projection lens, an optical platform, a high-precision mobile platform and a computer, wherein the collimator lens, The LCD panel, the projection lens and the high-precision mobile platform are sequentially clamped and fixed on the optical platform along the axial direction. The LCD panel is connected to the computer, and the LCD panel displays the stripe pattern generated by the computer. The cold The light emitted by the light source is irradiated on the LCD panel after passing through the collimating lens, and the stripe pattern displayed on the LCD panel is projected onto the reference plane or the surface of the object to be measured loaded on the high-precision mobile stage, There are two CCD cameras, which are symmetrically arranged on both sides of the LCD panel, and are used to capture the intensity of the fringe pattern projected on the reference plane on the high-precision mobile platform or the surface of the object to be measured.

As a further improvement of the utility model, the stripe pattern is an adjustable sinusoidal stripe pattern.

The utility model combines projection moiré and LCD phase shift technology. Using an incoherent cold light source and an LCD virtual grating to project sinusoidal fringe patterns onto the surface of the object under the field of view of the CCD camera, the LCD panel is connected to the computer through the liquid crystal display control interface to generate sinusoidal fringe patterns and phase changes to achieve adjustable raster pattern. The traditional sinusoidal fringe pattern is generated by the interference of two laser beams. The speckle noise generated by coherent light will affect the intensity distribution of the sinusoidal fringe pattern, reducing the measurement accuracy of the entire system, and the formed grating pattern cannot be adjusted. The unique optoelectronic properties of LCD panels make them ideal for use as controllable sinusoidal transmission gratings. By setting parameters such as the pattern area of the LCD panel, the period of the sinusoidal stripes, and the increment of the phase shift, it is easy to obtain the required sinusoidal stripe pattern.

The utility model adopts a different projection and imaging mechanism from the existing measurement system, and the cold light source is vertically projected onto the surface of the device to be tested through the LCD panel to ensure the uniformity of the projection intensity of the entire light field. At the same time, the left and right double-sided CCD imaging structure is adopted, which can eliminate the problem of not being able to capture the pattern in the partial shadow area caused by the single-side CCD, and can also eliminate the influence of specular reflection, and provide more moiré fringe information to improve measurement accuracy.

Compared with the existing measuring system, the utility model has the following advantages:

First, the utility model adopts the method of vertically projecting the cold light source onto the reference plane, so that the contrast of the stripes is better, and the photoelectric characteristics of the LCD panel will not be affected by the temperature.

Second, the utility model adopts a double-sided CCD tilting imaging mechanism, which can effectively eliminate the specular reflection of the chip surface and the object surface shadow phenomenon caused by poor contrast that cannot be solved by single-sided CCD imaging, and expands the measurable range of objects.

Its three, the utility model adopts the test technology based on LCD phase shift. The LCD panel is connected to a computer through a liquid crystal display control interface to generate sinusoidal fringe patterns and phase changes to achieve adjustable grating patterns.

Fourthly, the utility model adopts the full-field measurement technology, and the measurement area, measurement accuracy and measurement speed are all greatly improved, and can realize the requirements of large-area, high-precision real-time and fast measurement required in today's packaging and testing.

Description of drawings

Fig. 1 is the optical geometry schematic diagram of the projection and image acquisition system in the utility model.

Figure 2 is the layout and device diagram of the entire three-dimensional coplanarity measurement system. Among them, 1 is a cold light source, 2 and 4 are left and right CCD cameras, 3 is a collimator lens, 5 is an LCD liquid crystal panel, 6 is a projection lens, 7 is an optical platform, 8 is a high-precision mobile platform, and 9 is a computer.

Detailed ways

The utility model will be further described below in conjunction with the accompanying drawings and specific embodiments. In this embodiment, the object to be tested is a BGA solder ball, but it can also be substrate flatness in other packaging forms.

The projection moiré coplanarity three-dimensional measurement system of the utility model includes a cold light source 1, two left and right CCD cameras 2 and 4, a collimator lens 3, an LCD liquid crystal panel 5, a projection lens 6, an optical platform 7, and a high-precision mobile platform 8 and computer9.

The collimator lens 3 , the LCD panel 5 , the projection lens 6 and the high-precision mobile stage 8 are clamped and fixed on the optical platform 7 sequentially and linearly.

The cold light source 1 produces a beam of parallel light through a collimator lens 3 and irradiates it onto the LCD panel 5 , and a sinusoidal fringe pattern is generated on the LCD panel 5 , and the sinusoidal fringe pattern is focused and projected onto a reference plane through a projection lens 6 . The sinusoidal fringe pattern generated by the computer 9 on the LCD panel 5 is digitally phase-shifted, and the reference plane or the surface of the object to be measured is loaded on a high-precision mobile platform 8, which can precisely adjust its position to the field of view of the CCD cameras 2 and 4 Down. The intensity of the sinusoidal fringe pattern projected onto the reference plane or the surface of the object to be measured is captured by the CCD cameras 2 and 4, and the phase value φ(x, y) on the reference plane or the surface of the object to be measured can be obtained. Then calculate the phase difference Δφ(x, y) corresponding to each coordinate value on the reference plane and the surface of the object to be measured, and finally calculate the height value h(x, y) of the surface of the object to be measured under the field of view.

Since the transparency of the LCD panel 5 is easily affected by high temperature, a cold light source 1 with a power range of 0-150w (other powers can also be used) is used. The cold light source is vertically projected onto the surface of the object under test (BGA solder balls) through the LCD panel 5 .

The focal length of the collimator lens 3 adopted in the utility model is 50 mm (other focal length values can also be used), and it is installed behind the cold light source 1 to produce parallel light to irradiate on the LCD panel 5 . The reference plane or the surface of the object to be measured is loaded on the high-precision mobile stage 8 so as to accurately move the measured surface to the field of view of the CCD cameras 2 and 4 .

The LCD panel 5 is controlled by the computer 9 to generate the fringe pattern and the image capture of the CCD cameras 2 and 4 . The LCD panel 5 is connected to a computer 9 to directly generate sinusoidal fringe patterns and phase changes to achieve adjustable grating patterns. Using the four-step phase shift technology, the sinusoidal fringe pattern generated by the computer 9 on the LCD panel 5 is subjected to four-step digital phase shift, and the phases are 0, π/2, π, 3π/2 respectively. Calculate the phase value φ(x, y) on the reference plane or the surface of the object to be measured by the following formula.

$\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; tan</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; [</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ]</span>$

Among them, I ₁ (x, y), I ₂ (x, y), I ₃ (x, y), I ₄ (x, y) represent the phases are 0, π/2, π, 3π/2 respectively Intensity pattern of sinusoidal fringes.

In this embodiment, the sinusoidal stripes projected onto the surface of the BGA solder ball are deformed as the height of the solder ball surface changes. By detecting the deformed sinusoidal fringe pattern, combined with phase-shift analysis techniques, it is possible to obtain three-dimensional measurements of the surface of a rather large BGA solder ball. The coplanarity of the BGA solder ball surface can be reliably obtained by calculating numerous solder ball height values.

In this embodiment, the entire measurement system is controlled by the computer 9, including the movement of the mobile platform 8, the generation of the pattern of the LCD panel 5, the realization of phase shift, and the acquisition and post-processing of images. The image acquisition and post-processing adopt the fringe pattern received by the CCD cameras 2 and 4 to digitize the pattern through the image acquisition card, and the converted image signal is received and processed by the computer 9 . The image processing software performs phase shift calculation, unpacking calculation, etc., and finally obtains the topography information of the measured BGA solder ball surface on the computer 9 .

Claims (2)

1. A BGA coplanarity measurement system based on projection Moiré principle, is characterized in that, comprises cold light source (1), collimator lens (3), CCD camera (2,4), LCD panel (5), projection lens (6), optical platform (7), high-precision mobile stage (8) and computer (9), wherein, The collimator lens (3), LCD panel (5), projection lens (6) and high-precision mobile platform (8) are clamped and fixed on the optical platform (7) in sequence along the axial direction, and the LCD panel (5 ) is connected to the computer (9), the LCD panel (5) displays the fringe pattern generated by the computer (9), and the light emitted by the cold light source (1) passes through the collimator lens (3) irradiate on the LCD panel (5), and project the fringe pattern displayed on the LCD panel (5) onto the reference plane or the surface of the object to be measured loaded on the high-precision mobile stage (8), the There are two CCD cameras (2, 4), which are symmetrically arranged on both sides of the LCD panel (5), and are used to capture the fringe pattern intensity projected on the reference plane on the high-precision mobile platform (8) or the surface of the object to be measured. 2. The coplanarity measuring system according to claim 1, wherein the fringe pattern is an adjustable sinusoidal fringe pattern.

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