Metal fusion bonding – Process – With pretreating other than heating or cooling of work part...
Patent
1995-02-10
1998-04-07
Bradley, P. Austin
Metal fusion bonding
Process
With pretreating other than heating or cooling of work part...
228211, 228 42, B23K 3102, B23K 3538
Patent
active
057354510
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of Technology
This invention relates to a brazing technology that uses a brazing material to bond components, and more particularly to a soldering method and an apparatus that are suitable to soldering applications in fine pitch areas, such as in bonding electronic components to a printed circuit board.
2. Background Technology
Traditionally, the flow method and the reflow method have been used as the soldering methods most suitable for industrial mass production. For example, when the flow method is used for mounting components onto a printed circuit board (hereafter referred to as "substrate"), the substrate on which components have been placed is coated with flux, and then soldering is achieved by passing said substrate through a molten solder bath. In the reflow soldering method, a mixture of flux and soldering paste is printed onto the part of the substrate on which components are to be soldered. Then, after the components are placed on the substrate, soldering is achieved by passing said substrate through a heating oven called a "reflow oven." However, it is difficult to stably produce a uniform coating of flux on the bonding surface. For this reason, this coating step has become a major obstacle to achieving automation, as substrate patterns have become finer and assembly density has increased. Furthermore, in both methods, the residual flux on the substrate is corrosive, and thus, it is necessary to rinse the substrate after soldering. Additionally, when soldering a TAB substrate to a liquid crystal panel, the risk exists that the flux may splash and contaminate the polarizing film. Consequently, it is necessary to attach a protective film to the polarizing film beforehand, and to remove it after soldering is finished. This requirement increases the number of process steps, time, and labor, resulting in increased manufacturing costs.
Known methods of removing organic substances, such as flux, include the wet rinse method which uses an organic solvent, and the dry rinse method which removes organic substances by causing a chemical reaction in them through irradiation with ozone, or ultraviolet light, etc. However, the wet rinse method requires an additional rinsing process for removing the rinsing agent after the organic substances have been rinsed off, a process for drying the substrate, and a stationary facility for performing these processes. These additional requirements necessitate a massive amount of time and labor and result in increased manufacturing costs. On the other hand, thorough rinsing cannot be expected in the dry rinse method since it is difficult to completely remove organic substances possessing especially large molar weight.
To avoid these problems, no-rinse fluxes containing very little or no active species, such as chlorine, have been in use recently. However, because these fluxes possess poorer wettability than conventional fluxes, they have raised concerns that the resulting solder may be incomplete or may possess insufficient bonding strength.
Furthermore, when components must be soldered on both sides of a substrate, the heat treatment applied during the process up to that point causes the formation of an oxide film (CuO) on the surface of copper pads and electrodes, along with the loss of even the initial level of wettability, and, in some cases, leads to increased contact resistance during soldering.
Published Japanese patent application No. H03-174972 discusses a method which obtains excellent adhesion of a soldering material to a substrate. In this method, the substrate surface is coated with the soldering material, after using an argon gas atmosphere in vacuum to generate an electrical discharge, and this discharge is used to remove impurities from the surface of the substrate and to improve its wettability. However, this method requires a vacuum pump and a vacuum chamber for obtaining the vacuum atmosphere, making the overall equipment large and complicated. Furthermore, argon, the gas used, does improve the wettability between th
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Anan Makoto
Asano Yasuhiko
Kurashima Yohei
Kurashina Osamu
Miyakawa Takuya
Bradley P. Austin
Knapp Jeffrey T.
Seiko Epson Corporation
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