Solder Joint Inspection Research Articles

Thermal-Stress Analysis of SOIC Packages and Interconnections

Thermal stresses in surface-mounted small-outline integrated-circuit (SOIC) assemblies have been studied by the finite-element method. Emphasis is placed on the effects of solder-joint geometry on package and interconnection reliability. In addition, the problem of voids in solder joints is addressed. Seven different solder-joint geometries and six different sizes of voids are considered. It was found that the effect of voids in the solder joint is to increase the stresses acting on it. Furthermore, it is concluded that the results presented herein can provide guidelines for solder-joint inspection.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Feature selection for automatic visual inspection of solder joints

In this paper, three successive feature reduction methods are employed to select good features for the automatic visual inspection of solder joints. This reduction strategy includes (1) a stability test to remove the features with unstable performance, (2) a separability examination to select the features with good classification capabilities, (3) a correlation analysis to delete the redundant features. Three sets of features are implemented in this feature reduction work: (1) a circular sub-area feature set is related to the intensity conditions within distinct areas in the joint image, (2) a moment of inertia feature set is based upon the intensity of pixels and their relative position in the image plane, (3) a surface curvature feature set analyses the three-dimensional joint topology. Initially 50 features are formulated based on the above strategy. The reduction technique deletes 39 features from this set because of instability, poor performance, and high correlation with other features. Finally, the remaining 11 feature are tested and shown to be superior to state-of-the-art identification methods.

A tiered-color illumination approach for machine inspection of solder joints

An experimental color vision inspection system for the detection of solder joint flaws on printed circuit boards is described. A tiered lighting arrangement is used to generate color contours on the solder joint for the detection and classification of defects including no solder, insufficient or excess solder, poor wetting of component leads or solder pad, and faults due to improper insertion of component leads. Each type of defect gives rise to a characteristic pattern of color contours which are processed using binary image techniques on each color plane of the image. Geometric descriptors measuring the shape of the color contours and the color level intensities of the solder joint images are used to identify each defect class. Statistical distributions are determined for each of the good and defective joint classes, from which a flaw detection and classification tree is derived. The performance of the system was tested on samples of commercially manufactured, wave-soldered circuit boards. >

Parts inspection by laser beam heat injection

When a pulse of laser radiation falls on a material surface, a certain amount of warming will occur which depends upon the surface properties of the material, particularly upon its absorptivity. The amount of warming will also depend upon what is underneath the surface and especially upon the amount of mass which is available for the thermal energy to expand into. If the warming process is monitored by an infrared detection system, one has a ready means of determining whether or not two parts are alike in their surface properties or in their internal features. An automatic, non-contact system is described which uses this principle for the inspection of solder joints on printed wiring boards at rates of up to 10 joints per second. With minor changes, the inspection system can be used to repair defective joints and to manufacture new ones by the reflow of solder paste or performs. Extensions of the inspection method are described with regard to the testing of bonds in metal sheets and to the measurement of paint thicknesses on metals.

Automated visual inspection: 1981 to 1987

This bibliography lists journal publications, conference papers, research technical reports, and articles from trade journals on automated visual inspection for industry which were published during the years from 1981 to 1987. More than 600 references are included. References are organized into 13 categories according to subject matter. The categories are (1) books, (2) conferences and workshops, (3) general discussions and surveys, (4) inspection of printed circuit patterns, (5) inspection of solder joints, (6) inspection of microcircuit photomasks, (7) inspection of integrated circuits and hybrids, (8) inspection of other electrical and electronics components, (9) surface inspection, (10) X-ray inspection, (11) other inspection applications, (12) system components, and (13) inspection algorithms. References listed in each category are arranged in chronological order. The purpose is primarily to provide a complete bibliography for those interested in automated visual inspection. Some general observations have been made for the above areas of activity summarizing the advances that have taken place and the problems that remain to be solved.

Automatic solder joint inspection

The task of automating the visual inspection of pin-in-hole solder joints is addressed. Two approaches are explored: statistical pattern recognition and expert systems. An objective dimensionality-reduction method is used to enhance the performance of traditional statistical pattern recognition approaches by decorrelating feature data, generating feature weights, and reducing run-time computations. The expert system uses features in a manner more analogous to the visual clues that a human inspector would rely on for classification. Rules using these cues are developed, and a voting scheme is implemented to accumulate classification evidence incrementally. Both methods compared favorably with human inspector performance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Automation of solder joint inspection procedures utilizing laser induced infrared : Gary W. Fugate and Joe R. Felty. IEEE Trans. Compon. Hybrids mfg Technol.CHMT-10, 374 (1987)

Automation of solder joint inspection procedures utilizing laser induced infrared : Gary W. Fugate and Joe R. Felty. IEEE Trans. Compon. Hybrids mfg Technol.CHMT-10, 374 (1987)

Automation of Solder Joint Inspection Procedures Utilizing Laser Induced Infrared

In the rush to automate assembly flow in the fabrication and assembly of electronic equipment, great strides have been made in all areas with the exception of solder joint inspection and rework. This paper focuses on an attempt to automate, at least in part, the inspection of printed wiring assembly (PWA) solder joints. The use of laser and/or X-ray equipment is causing quite a stir in the industry due to the fact that there finally appears to be a technique that may allow for automation of one of the most labor intensive, inexact, and costly tasks in any PWA assembly operation--the visual inspection of solder joint quality. As the complexity of PWA's increase, the number and density of solder joints are increasing. This trend is resulting in decreased efficiency in the inspection process due to the shear number of joints to be inspected, operator fatigue, and the subjectivity of the entire inspection process. In areas where absolute quality is critical, such as military products, this declining inspection effectiveness is being compensated for by the incorporation of multiple inspection-rework loops. These techniques statistically should result in the identification of all defects on a given assembly. However, the impact of this multiple inspection process is one of total disruption to the assembly flow in an automated shop. Laser induced infrared (IR) inspection has been under investigation by Texas Instruments' Defense Systems and Electronics Group for the past several years. Our thrust has been aimed at the incorporation of this technique into the inspection of PWA's that are fabricated for military customers. Extensive efforts have been expended in the determination of the strengths and weaknesses of the technique in an attempt to augment the human element in the inspection process.

Certainty of measurement using an automated infra-red laser inspection instrument for PCB solder joint integrity

An analysis is presented of the basic principles governing the operation of Vanzetti's Li/6000 Laser/Inspect instrument for the automated inspection of solder joints on printed circuit boards (PCBs). The instrument operates by monitoring the infra-red emission from a solder joint which has received a short pulse of heat from a YAG laser. Theoretical expressions are established for the response of the instrument to defects, both in the bulk of the solder fillet and also at the surface, both for populated and unpopulated PCBs. The predictions, supported by measurements on unpopulated PCBs, show that enclosed voids in the solder fillet of a plated-through-hole PCB give an insignificant change in signal, but that blowholes on the inspection side, with vents greater than 0.07 mm in diameter, may be clearly discerned. The important effect enabling discrimination is that the vent acts as a black body absorber and radiator whereas the solder surface largely reflects the radiation.

Automatic visual solder joint inspection

An approach is described for the automatic inspection of solder joints on printed circuit boards. Common defects are identified in solder joints and a joint is classified as being good or belonging to one of the defective classes. The motivation for this classification is not just the detection of defective joints, but the desire to automatically take corrective action on the assembly line. The features used for classification are based on characteristics of intensity surfaces. It is shown that features derived from facets and Gaussian curvature are effective in the classification of solder joints using a minimum-distance classification algorithm. Class separation plots are shown to be useful for quickly studying individual effectiveness of a feature or pair of features in classification. Results show the efficacy of the described approach.