SE458837B - PROCEDURE TO REMOVE POLLUTION POLLUTANTS FROM A PURPOSE, EXAMPLE A CIRCUIT TO BE LOADED - Google Patents

Description

458 1D 15 20 25 857 ning - washing. Furthermore, decomposition products from the flux are avoided in connection with the purge at high temperature. The purpose of the present Lppfiming is thus to provide a method which effectively removes organic and inorganic residues before a soldering process without obtaining environmentally hazardous residues and with a more even temperature distribution.

The method according to the invention is then characterized as appears from the following patent claims.

DESCRIPTION OF THE FIGURES The proposed method will be described in more detail with reference to the accompanying drawing, in which Figure 1 schematically shows a known method described under "prior art", Figure 2 schematically shows the method according to the invention, Figure 3 shows a temperature diagram.

EMBODIMENTS The proposed method is shown schematically in Figure 2.

The flux step a) is carried out in the same way as in the known method according to Figure 1, i.e. the solder side of the circuit board 1 is sprayed with an effective flux of the above-mentioned composition. Possibly so-called foam fluxing can be performed. Denoted by 2 is a nozzle through which the flux in foam form is sprayed onto the solder side of the circuit board.

After the flux step a) follows the heating step b) in which the circuit board 1 is heated to cza IÜÜOC, for example by means of heat lamps. The heating has essentially three purposes, namely partly to concentrate the flux, partly to dissolve tin oxides etc. and partly to preheat the card before the subsequent soldering process.

According to the proposed method, the soldering process is not performed directly after the heating, but instead the washing is performed in step c). The washing then removes all contaminants before the onion broth and can therefore be carried out by means of water, optionally with the addition of some carrier and / or surfactant. To avoid a significant lowering of the temperature after the flux step, the water should have a suitable temperature, for example 70-80 ° C. The washing can optionally be performed in two steps, however, with the temperature maintained close to IOÛDC. During washing, there is a strong dilution of the corrosive flux residues and other contaminants and metallic surfaces on the solder side of the board are free of grease and oxides. In order to protect the metal surfaces against oxidation, these can in the second washing step be coated with a carrier / solvent and / or inhibitor, so-called surface protection.

Immediately after the washing step c) the soldering is carried out at a temperature of about ZSDOC with a molten lead-tin alloy in a known manner. Any residues that remain after the soldering process are harmless.

Flux scales, washing and surface protection can be performed with a so-called gap scales. Figure 3 shows a temperature diagram 80m illustrating the temperature change over the various steps a) - d). It appears that the solder surfaces of the circuit board can be obtained more evenly and longer with the present method (solid curve II) than with the previously known one (dashed curve I). In the known method a "temperature hump" is due to the soldering and washing in the last step, which gives a more shocking temperature change than in the present method. This is of course a disadvantage due to the risk of mechanical ruptures (cracking, cold soldering). With the present method, a slower heating and cooling of the solder material is achieved. It is therefore necessary that the washing step according to Figure 2c) has a sufficiently high temperature, so that the even heating is maintained.

HRS'

Claims (4)

f-458 857 10 PATENT CLAIMS A method of removing organic and inorganic residues from an object, for example a circuit board, which is to undergo a soldering process, which method comprises fluxing, heating and washing, characterized in that the method is carried out in successive steps: a) flussing with per se known chemical means for binding impurities on the object surface, b) heating to a certain temperature higher than the temperature at the flux to activate said surface, c) washing the surface with water, the temperature of which is substantially the same as the heating temperature after which , d) the soldering process takes place immediately after said washing. Method according to claim 1, characterized in that the solder surfaces during the washing step c) are coated with a surface protection to counteract oxidation of the surfaces. Method according to claim 1 or 2, characterized in that, in the case that the soldering process takes place at a temperature of ZSOOC, the heating in said heating step takes place to about 10 ° C and that the washing then takes place with water, the temperature of which is between 70 ° C and 8000- 4. A method according to claims 2-3, characterized in that the washing is performed in two steps with substantially the same water temperature, wherein said coating of surface protection takes place in the later washing step.