It is very often that top fillet profiles of Pb free solder connected with QFP (Quad Flat Package) leads fluctuate more than those of Pb eutectic solder and have coarse surface roughness. The fluctuation and surface roughness make it difficult to carry out the feature extraction of the top fillet. The purpose of the present study is, therefore, to extract the top fillet profile characteristics using a simple image processing. Pb free solder used in the present study was Sn-3.5Ag-0.7Cu. QFP leads plated with Sn-10Pb or Au/Pd/Ni were used as an inspection object. As a prior work, we investigated an appropriate observing direction, that is, the camera angle to obtain highlight in the vicinity of the top fillet (the side of QFP lead edge) and the distribution (fluctuation) of the camera angle were examined, because the camera angle was closely related with the wetting angle at the top fillet. The good profiles of the top fillet could be judged, i.e., the top fillet profiles with a proper wetting angle were decided by whether or not a certain highlight area (island) was observed. It was found that the judgement was possible if the size of the island (number of pixels with level 1 after binarization) was adequately regulated.
This paper presents the suitability of solders for solder-coating of surface mount wiring boards. We found that the degradation of solderability is due to the growth of Cu-Sn intermetallic compounds and subsequent oxidation of the Cu. Adding Cu to the solder-coating inhibits the growth of Cu-Sn compounds by reducing Cu diffusion. Adding Ge or In prevents the oxidation of Cu by forming a Ge- or In-rich layer on the surface. Solder-coatings with Sn-Pb solder containing these elements have good solderability.
Thermosonic flip-chip bonding is a low cost assembly method and has high productivity. In this bonding, the bump formed on a device chip is directly bonded to a substrate electrode in a short time. This paper describes the effect of bump condition on bondablity of flip-chip bonding. Experiments were carried out using a chip with aluminum electrodes and a gold-plated ceramic substrate. Two kinds of bumps that differ in strength and deformation were compared in flip-chip bondability. As a result, the highly deformed bump with high strength made bond strength between the bump and substrate electrode stronger. Additionally, bump deformation after flip-chip bonding and bond strength between the bump and chip electrode did not depend on the bump condition.
In this study, the effect of the laser beam irradiation method on the deformation characteristics of laser forming for plastic material by YAG laser was experimentally investigated. In the case of area irradiation method, bending angle becomes smaller after the irradiation, since the amount of bending-down is large during the irradiation. Therefore, even if the number of laser beam irradiation increases, large bending angle can not be obtained. On the other hand, in the case of scan irradiation method, the bending angle becomes larger after the irradiation, since the amount of bending-down is small during the irradiation. As a result, the scan irradiation method makes it possible to obtain large bending angles up to 90 degrees by increasing the number of laser scan. Therefore, in order to obtain larger bending angles, the scan irradiation method is more effective than the area irradiation method.
Welding process of thin stainless foil, the thickness of which was 40 μm, was studied using a single mode Yb-fiber laser with a CW output of 40W at maximum. The spot size of the laser beam used for a series of welding was measured by a beam profiler equipped with a rotating knife-edge and a photodiode. The spot size of approximately 10 μm in diameter at 1/e2 power density of the value at beam center was obtained by a focusing lens, the focal length of which was 55mm. The power density up to 108W/cm2 was provided by a laser power of only 40W. The transition of beam absorption process between conduction type and keyhde type was discussed based on back-reflected laser energy, which was estimated by a laser energy passing through the metal foil, WP, and a laser energy coupled to the specimen, WC. The former was directly measured using an integration sphere. The latter was estimated by a calculation based on the line heat source model. The threshold power density by the single mode fiber laser for deep penetration welding was 2 orders higher than that of macro welding, however, deep penetration was maintained up to at least 920mm/s at 25W resulting efficient and ultra-fine keyhole welding of stainless foil, the thickness of which was 40 μm, without humping.
In this research, we examined the method that separates the material from the printed circuit board by the proof scale heat-treatment. The size of the printed circuit board (PCB) used for the examination was about 150 mm × 200 mm, and PCB was executed heat-treatment by two kinds of shape as received (Sample-A) and crushed (Sample-B) by hammarcrasher. The following result was obtained. The organic resin and also omine were removed by the heat treatment in both cases. In Sample-B heat-treatment, though combustion was done with stability, however, the temperature rises locally so that the organism in the board crushed by the high contact with oxygen may burn instantaneously and the combustion residue melted solidifies. In Sample-A heat-treatment, the metallic collection rate in the combustion residue was higher than Sample-B, especially Cu and Ni are collected by 90mass% or more, and Ag, Au and Pb collected were twice larger compared with Sample-B. The residue in Sample-A could be crushed comparatively easily with hammarcrasher. Therefore, to make the crushing combustion residue concentrated of the metal in the printed circuit board adjust to metallic refinement process, it is thought that we should heat-treat the printed circuit board near as received.