JPS6219277B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in solid flux used when mounting components onto printed wiring boards. Conventionally, when components are soldered to a printed wiring board, this is done by a solder dipping method or an automatic soldering device. That is, first, flux is applied to the printed wiring board, then components are mounted at the required locations, the components are fixed by preliminary soldering, and then the lead wires of the components are cut with a cutter. Finally, final soldering is performed to firmly fix the parts. This method has been considered convenient in that it allows a large number of components to be soldered to a printed wiring board at the same time. However, in this conventional method, soldering must be performed twice: preliminary and final soldering.
It is time-consuming and wasteful in terms of process, and
For example, after pre-soldering the component lead wires,
Since it is cut to a length of about 2 mm, it is often cut together with a solder alloy, causing problems such as severe damage to the cutter. The inventors of the present invention have conducted various studies in order to eliminate all of the above drawbacks and make it possible to solder only once, and as a result, they have discovered a solid flex that can fix the legs of components to some extent before soldering, and hereby propose. It is something to do. The solid flux according to the present invention is used when mounting parts such as transistors on a printed wiring board, after inserting the legs (lead wires) of the parts to be mounted into the insertion holes provided in the printed wiring board, and before soldering. It is characterized in that it can be applied to the entire surface or a predetermined location on a wiring board, fixed, and then cut without pre-soldering the lead wires. The solid flux of the present invention is based on petroleum-based, vegetable oil-based, or mineral oil-based wax, to which organic acids having carboxyl groups, such as saturated fatty acids, unsaturated fatty acids, and antioxidants are added, and these are heated. It can be obtained by dissolving. Petroleum, vegetable oil, and mineral oil-based waxes that can be used in the present invention include, for example, paraffin wax, microwax, wood wax, carnauba wax, and mixtures thereof. Various types of these may be selected and used depending on the purpose, but for example, a melting point of about 100°C is preferable. If the organic acid is liquid at room temperature, it will have good compatibility with wax, but it will have poor component retention strength, and it will also affect oxidation stability, so it is preferable to use one that is solid at room temperature. Further, when the number of carbon atoms is 30 or more, component holding strength can be obtained, but compatibility may be impaired or solderability may be impaired, so organic acids having a carbon number of 30 or more are preferable. Since the amount of antioxidant used is small, it does not interfere with the fixing effect of wax etc., and as long as it can be used for this purpose, those used in conventional fluxes can be used as is. Unlike conventional rosin-based fluxes, that is, liquid or paste-like fluxes made of rosin resins, activators, organic solvents, etc., the flux according to the present invention is solid, so it can be applied to printed wiring boards by dipping. For example, the legs of a component to be mounted on a wiring board can be fixed to a certain extent - to the extent that the lead wires of the component can be cut without pre-soldering. If you cut the component lead wires in this way, there will be less damage to the cutter because there will be no solder on the lead wires, and in addition, when final soldering to fix the components, The above-mentioned solid flux melts sufficiently at the soldering temperature of around 200°C, so it also exhibits good solderability and provides a beautiful finish in appearance. The solid flux of the present invention may be applied to the entire surface of the printed wiring board after the components have been mounted, or may be applied only to predetermined locations. During soldering, a conventional flux may also be applied. The present invention will be explained in more detail with reference to Examples below, and unless otherwise specified, % in the Examples represents % by weight. Examples 1 to 5 Wax in each example listed in the table below,
Contains 90% each of three components: fatty acids and antioxidants.
%, 9.5%, and 0.5% to obtain the solid flux of the present invention.

[Table] The solid flux according to each example obtained in this way is applied onto a printed wiring board by dipping to fix the component, then the lead wire of the component is cut, and finally soldered. Components are attached to the printed wiring board by attaching them. After this component was mounted on the printed wiring board, the solder spreading rate, corrosion resistance, surface insulation resistance, and fixation of the component to the printed wiring board were examined. The results are summarized in the table below. The solder spreading rate was measured according to the JIS standard - flux test method.

【table】

[Table] As is clear from the above table, the solid flux of the present invention has good properties, and even when cutting lead wires for parts, the lead wires can be neatly cut to a length of about 1.5 mm. did it. As described above, by using the solid flux according to the present invention when attaching components to printed wiring boards, all the disadvantages of the conventional methods such as eliminating the trouble of pre-soldering and reducing cutter damage are eliminated, and the finishing The present invention has many advantages, such as excellent solderability and improved functionality of the printed wiring board after mounting components.

Claims (1)

[Claims] 1 Wax with a melting point of about 100℃, solid at room temperature, consisting of a fatty acid with a carbon number of 30 or less and an antioxidant,
A solid flux for soldering that can be applied before soldering to fix components to be mounted on a printed wiring board to the extent that the lead wires can be cut.