KR20030036976A - Device for detecting appearance of solder balls for bga package and method for setting optimum lighting condition thereof - Google Patents

Abstract

PURPOSE: A device for detecting appearance of solder balls for bga package and method for setting optimum lighting condition thereof are provided to increase reliability of inspecting equipment by detecting whether a lighting condition is suitable even if time passes or inspection surroundings vary before an inspection is performed on a real object. CONSTITUTION: A reference sample is transferred from a reference sample storing unit to an inspecting unit according to a start signal of inspection. The reference sample is measured in the inspecting unit according to an arbitrary lighting condition. A difference(measurement error) between the measurement value of the reference sample and a known real value of the reference sample is calculated. The measurement error is compared with an allowable error to obtain an optimum condition regarding the brightness of lighting.

Description

BA device for detecting appearance of solder balls for BGA package and Method for setting optimum lighting condition

The present invention relates to a BGA solder ball shape inspection device and a method for setting the optimal illumination of the inspection device, and more particularly, in the semiconductor appearance inspection process of the solder ball appearance of the BGA product using a CCD camera, the reference state is used to the illumination state. It relates to a method for effectively setting the optimal illumination brightness by minimizing the error of the measured value and the inspection device of the solder ball shape using the reference sample.

Ball grid array (BGA) is a kind of semiconductor package that has solder ball as an external connection terminal. When such a BGA product is mounted on a PCB board, defects in the appearance such as deformation of the connection terminal exist. Is mounted in an incomplete state, causing contact failure and the like, which causes additional failure in terms of reliability. Therefore, good quality semiconductor products that have completed all the characteristic tests are inspected for appearance before shipment, and the products with poor appearance conditions are selected and treated as defective. One of the most important inspection items in the external inspection process is to inspect the external connection terminals of each product.

In general, the external appearance inspection of the solder ball is performed using a CCD (Charge Coupled Device) camera. Referring to the conventional inspection method illustrated in FIG. 3, first, a BGA product physical part of a product physical storage part is moved to an inspection part, and the inspection part Each product moved to is taken by the camera to obtain an image of the shape of the solder ball and is inspected according to a predetermined standard. Next, according to the determination criteria set in the output unit, the finished product is classified and output as good or bad.

When explaining the process of acquiring an image of the shape of the solder ball in the appearance inspection process of the solder ball as described above, for example, it illuminates the surface of the solder ball to be inspected light, such as a ring-light, using a CCD camera The light reflected from the solder ball is detected and the reflected image is displayed on the monitor. Here, the lighting state supplied during the solder ball external inspection of the BGA product is the most influential factor on the accuracy of the measured value. When too dark or bright lighting is supplied to the surface of the solder ball, the inspection of the appearance of the solder ball causes a large error in the measured value.

4A and 4B schematically show the structure of a conventional solder ball contour inspection apparatus using a ring light illuminating apparatus. FIG. 4A is a side view of the inspection apparatus and FIG. 4B is a top view of the inspection apparatus. FIG. 5 is a view schematically illustrating a process in which light reflected from a solder ball is displayed as an image, and shows the shape of the solder ball and an image obtained through a camera. As such, in order to obtain the correct image of the solder ball shape as an object in the inspection process of recognizing the shape of the solder ball as a camera image using the CCD camera and reading out whether each solder ball is deformed, appropriate illumination must be supplied to the surface of the solder ball.

6A to 6C show solder ball images according to brightness of illumination, and FIG. 6A shows excessively bright light, FIG. 6B shows too dark illumination, and FIG. 6C shows images of solder balls obtained when illumination is appropriate. As can be seen in Figure 6, the image form obtained by the camera according to the state of the illumination supplied to the solder ball as the subject there are many differences. Of course, the error of the measured value is also severe. 7 is a graph showing the measurement error of the solder ball diameter according to the brightness of the light after measuring the diameter of the solder ball using a reference sample while changing only the brightness of the illumination in the same condition all other conditions in the inspection apparatus to be. As can be seen from this graph, even though there is an error in the measured value depending on the brightness of the lighting, the existing inspection apparatus always has the same lighting conditions as the first set values in the state that the lighting conditions are determined and set once. The test proceeds while maintaining the.

Therefore, according to the conventional inspection method, even if a lapse of time or a change in the inspection environment occurs, there is no verification procedure for whether the preset lighting conditions are actually appropriate. Therefore, the inspection is carried out under the wrong lighting conditions, there is a fear that the reliability of the inspection equipment. That is, in the existing inspection method, there is no method to automatically check whether a lighting condition having a direct influence on the measured value is suitable at regular intervals, so there is a problem that cannot be easily detected even if the brightness of the lighting is incorrectly set. Done.

1 is a view showing a series of steps for the solder ball shape inspection method according to the present invention.

2 is a flowchart of a method for calculating an optimal lighting condition according to the present invention.

3 is a diagram illustrating a series of steps for a conventional method for inspecting a solder ball detective.

4A and 4B schematically show the structure of a conventional solder ball contour inspection apparatus using a ring light illuminating apparatus. FIG. 4A is a side view of the inspection apparatus and FIG. 4B is a top view of the inspection apparatus.

FIG. 5 is a view illustrating a process in which light reflected from a solder ball is displayed as an image, and shows a shape of the solder ball and an image obtained through a camera.

6a to 6c show solder ball images according to the brightness of illumination, and FIG. 6a shows an image of solder balls obtained when the illumination is too bright, FIG. 6b when the illumination is too dark, and FIG. 6c when the illumination is appropriate. to be.

7 is a graph showing the measurement error of the solder ball diameter according to the brightness of the illumination.

Accordingly, the present invention is to propose a method that can effectively set the optimal illumination brightness in order to minimize the error of the measurement value due to the illumination state in the inspection of the solder ball of the BGA product.

According to the present invention, a method for inspecting a solder ball shape of a BGA product includes moving a product physical product disposed in a product physical storage part to an inspecting part, inspecting a solder ball shape of the product real product in the inspecting part, and inspecting the product actual product. In the solder ball shape inspection method comprising the step of determining whether the good or bad according to a predetermined criterion, before the start of the step of moving the actual product to the inspection unit, according to the signal of the inspection start of the reference sample storage unit A reference sample arrangement step of moving from the inspection unit to the inspection unit, the reference sample measurement step of measuring the reference sample under an arbitrary illumination condition in the inspection unit, and the measured value of the reference sample measured in the reference sample measurement step and the known reference sample. Calculate the difference (measurement error) between the actual value and compare the measurement error with the allowable error value And an optimum condition setting step of obtaining an optimum condition for brightness of illumination.

The inspection method according to the present invention includes a series of steps for setting an optimal condition of illumination using a reference sample according to a signal of the inspection start before the beginning of moving the product to the inspection unit, for example, a predetermined period (E.g., before each LOT test begins), the tester is configured to measure the reference sample according to each condition while varying the brightness of the illumination using a reference sample that is known to the correct value. Here, the reference sample refers to a sample manufactured in a form similar to the actual product, and refers to a sample that can be used as a constant standard because the value of each solder ball is accurately measured in advance and already knows its value. Therefore, by comparing the actual measured value obtained by measuring the reference sample under a certain condition with the known reference value, it is easy to calculate the measurement error under the condition.

Next, the measured values of the reference samples measured for each lighting condition are compared with the actual values to find the lighting condition having the lowest measurement error. In detail, the procedure is repeated if the measurement error, which is the difference between the measured value of the reference sample and the actual value of the reference sample, is greater than the allowable error value. If the measurement error, which is the difference between the measured value of the reference sample and the actual value of the reference sample is less than the allowable error value, the inspection process for inspecting the real product of the product after the illumination condition measuring the reference sample is set to the optimum condition This is done.

In addition, according to the present invention, the solder ball external inspection device is a product real storage unit in which the actual product is placed, the inspection unit including a lighting device such as a ring light illumination device and the CCD camera and the actual product in which the solder ball shape is inspected in the inspection unit Including an output unit for determining good or bad according to the criteria, and further, in order to effectively perform the inspection method of the present invention, a reference sample may be arranged, if necessary, pick up the reference sample (Pickup) to move to the inspection unit After calculating the optimum condition of the illumination brightness by measuring the reference sample in the inspection unit, it is characterized in that it further comprises a reference sample storage unit configured to be stored by moving back to the original storage position.

Hereinafter, a method of setting an illumination condition according to the present invention will be described with reference to FIG. 1.

1 shows a test method according to the present invention composed of a series of steps. According to the present invention, a process of setting an optimum condition of illumination by first inspecting a reference sample prior to external appearance inspection of a solder ball of a product real thing is included. In other words, the inspection procedure of the actual product is the same as the existing inspection method, but the procedure for setting the optimal lighting conditions required for the inspection in order to increase the accuracy of the measured value before starting the inspection operation for such an object in earnest. Going through. The following describes the process of setting the optimal condition for lighting using a reference sample and the process of inspecting the actual product in a series of steps.

In step 1, upon receiving the signal of starting the test, the reference sample is moved from the reference sample storage unit to the inspection unit, and the inspection unit fixes the position in the test standby state.

In step 2, the reference sample is measured under any illumination condition.

In step 3, the measurement error is calculated based on the measured value measured in step 2 and the actual value of the known reference sample, and the result is used to obtain the optimum condition for the brightness of the illumination.

In step 4, the reference sample is moved from the inspection unit to the reference sample storage unit, and the product is transferred from the physical storage unit to the inspection unit.

In step 5, the product is held in the inspection standby state, and then the lighting of the system is fixed to the optimum condition obtained in step 3, and the product is inspected.

In step 6, the product has been inspected in step 5 is moved to the output unit, and according to the judgment criteria, the output unit is separated into good quality and defective output.

Through the above series of steps, it is possible to automatically check whether a lighting condition having a direct influence on the measured value is suitable at regular intervals, thereby increasing the reliability of the inspection apparatus. In particular, in step 3 above, by examining the measurement error of the reference sample, a stable illumination condition in which the measurement error of the reference sample falls within the allowable range in each illumination condition while automatically changing the brightness of the illumination step by step from the initial illumination condition. After obtaining, the condition can be applied as it is to the inspection of the real thing.

2 is a flow chart illustrating in more detail a method for calculating an optimal lighting condition according to the present invention. Here, "M" means a measured value measured by the inspection unit under a certain illumination condition, "R" means the actual value (reference value) of the reference sample. Further, the difference between the measured value M and the actual value R of the reference sample, that is, | M-R | means a measurement error, and "A" represents an acceptable error value.

Referring to the flowchart of FIG. 2, step 3 of FIG. 1 will be described in more detail. After the reference sample is moved to the inspection unit, the reference sample is measured under an initial illumination condition (eg, 100% of illumination brightness). The difference between the measured value M thus obtained and the actual value R, that is, the measurement error (| M-R |), is calculated and compared with the allowable error value (A). If the measurement error (| M-R |) is larger than the allowable error value A, step 2 of FIG. 1 is repeated. At this time, the brightness of the illumination is adjusted to an arbitrary size (eg 10% reduction). After a new measured value (M ') is obtained in step 2 with the newly adjusted lighting conditions (i.e. 90% of the brightness of the light), then again in step 3 the measurement error (| M'-R |) The value A is compared. At this time, if the measurement error (| M'-R |) is larger than the allowable error value (A), the above process is repeated again. Therefore, the lighting condition is changed to another lighting condition (that is, the lighting brightness is 80%). The reference sample will be measured again. In this way, it can be repeated several times until the measurement error is smaller than the allowable error value. In the above example, if the difference between the measured value of the reference sample (eg M '') and the actual value R, i.e. measurement error (| M ''-R |) measured at 80% of the illumination brightness, is acceptable When it is smaller than the error value A, the illumination brightness (80%) is fixed at the optimum condition.

When the optimum conditions are set in the above manner, the next step is to move the reference sample back to the reference sample storage section, and then the actual product inspection process is performed.

In addition, in the present invention, since the reference sample is used, a separate reference sample storage unit for placing the reference sample in a position adjacent to the inspection unit is required. The reference sample storage unit, the reference sample may be arranged, if necessary, the reference sample is picked up (Pickup) and moved to the inspection unit, by measuring the reference sample in the inspection unit after calculating the optimum condition of the illumination brightness, and then stored the original It is configured to be moved to a location for storage.

Solder ball contour inspection method according to the present invention, unlike the conventional solder ball contour inspection method, the difference between the measured value and the actual value using the reference sample before the start of the step of moving the actual product to the inspection unit and the allowable error By comparing the values, an optimum condition setting step of obtaining an optimum condition for the brightness of the illumination is included. Through this process, even if time elapses or a change in the inspection environment occurs, verification that the lighting conditions are actually appropriate is performed before the actual inspection process of the product, thereby increasing the reliability of the inspection equipment.

In addition, according to the present invention, the solder ball external inspection apparatus is provided with a separate reference sample storage unit for placing the reference sample in a position adjacent to the inspection unit, it is possible to perform the inspection method according to the present invention more effectively.

Claims (3)

The first step of moving the product physical placed in the product physical storage unit to the inspection unit, the second step of inspecting the solder ball shape of the product physical in the inspection unit and the finished product in accordance with certain criteria to determine whether the good or defective In the inspection method of the solder ball shape comprising a third step of determining, before the start of the first step, A reference sample arranging step of moving the reference sample from the reference sample storage section to the inspection section according to the signal of the inspection start; A reference sample measuring step of measuring the reference sample under an arbitrary lighting condition in the inspection unit; And The difference (measurement error) between the measured value of the reference sample measured in the reference sample measurement step and the actual value of the known reference sample is calculated, and the measurement error is compared with the allowable error value, so that Setting an optimum condition for obtaining an optimum condition; Solder ball shape inspection method comprising a. The method of claim 1, wherein the setting of the optimum condition comprises: adjusting the initial illumination brightness when the measurement error, which is the difference between the measured value measured by the inspection unit and the actual value of the reference sample, is greater than the allowable error value. If the measurement step of the reference sample is repeated and the measurement error, which is the difference between the measured value of the reference sample and the actual value of the reference sample, is smaller than the allowable error value, the illumination condition of measuring the reference sample is set to an optimal condition. Solder ball shape inspection method characterized in that the first step is performed. An inspection unit including an illumination device such as a product physical storage unit, a ring light illuminating device, and a CCD camera, and an output unit for discriminating the actual product of the product whose solder ball shape is inspected by the inspection unit as good or defective according to a certain judgment standard. In the solder ball outline inspection apparatus comprising: A reference sample may be arranged, and if necessary, the reference sample may be picked up and moved to the inspection unit, and the inspection unit may measure the reference sample to calculate the optimal condition of illumination brightness, and then move it back to its original storage position for storage. Solder ball contour inspection apparatus further comprises a reference sample storage configured to be enabled.