FI89685B - METHOD ATT I EN LOEDPROCESS AVLAEGSNA ORGANISKA OCH OORGANISKA RESTER - Google Patents

Description

89685

The present invention relates to a process for removing organic and inorganic residues before soldering. The method is applied, for example, to the mechanical soldering of printed circuit boards.

A previously known method for removing residues by mechanically soldering circuit boards in large series 10 is shown in the attached Figure 1.

Is first made in step a) of the circuit board 1 to be soldered side processing flux for removing impurities, such as tin oxide, the acid residues and the fat. The flux treatment is performed in a so-called flux wave 15 by means of a nozzle 2. The melting agent usually consists of a solution containing disintegrants, organic acid, carriers, solvents and a surfactant.

After the flux treatment step a), heating takes place in step b) to dry the circuit board 1. The plates are usually heated to approximately 100 ° C.

After step b), the actual soldering of the circuit board 1 is performed c) with a fluid alloy of lead and tin at a temperature of approximately 250 ° C, and after soldering, in step d) a washing takes place to remove flux residues and their decomposition products. Washing is usually done with a solution containing freon (95%) which removes ____ flux residues. Given the environmental factors that have recently become significant, 30 this method is not satisfactory. If water-soluble fluxes are used, water should be used for washing to remove flux residues. It is very uncertain whether corrosive flux residues can be completely removed (from the capillaries).

35 According to the method proposed here, the washing is performed 8 S 6 8 5 2 before and not after the next stage of soldering. In this case, the use of freon can be avoided and, moreover, a more even temperature rise can be obtained during soldering and washing. In addition, the presence of melt decomposition products 5 during high temperature soldering is avoided.

It is therefore an object of the present invention to provide a method for efficiently removing organic and inorganic residues before soldering without forming environmentally hazardous residues while maintaining a more uniform temperature rise.

The characteristic features of the method according to the invention appear from the following claims.

The proposed method will be described in more detail with reference to the accompanying drawing, in which Figure 1 schematically shows the known method described above; Fig. 2 schematically shows a method according to the invention, and Fig. 3 is a temperature curve.

The proposed method is shown schematically in Figure 2.

The flux treatment step a) is carried out in the same manner as in the case of the known security method according to Fig. 1, i.e. the solderable side of the circuit board 1 is sprayed with an efficient flux having the above-mentioned composition. The flux treatment can possibly be performed by a so-called foam method. The nozzle through which the foam melt is sprayed on the soldered side of the circuit board 30 is indicated by the number 2.

After the flux treatment step a), a heating step b) follows, in which the circuit board 1 is heated to a temperature of approximately 100 ° C, for example by means of heat lamps. The heating has three main purposes, namely the concentration of the flux, the dissolution of tin oxides, etc. and the preheating of the plate? 3685 3 before the next stage soldering.

According to the proposed method, soldering is not performed immediately after heating, but washing is performed in step c). In this case, the washing removes all impurities before soldering and can therefore be carried out with water, possibly with the addition of a carrier and / or a surfactant. To prevent a significant drop in temperature after the melt treatment, a water temperature is suitable, for example 70-80 ° C. The washing can possibly be performed in two steps, however, keeping the temperature close to 100 ° C. when washing takes place corrosive agent Sun-track residues and other impurities from a strong dilution, and the sheet metal to be soldered side surfaces are free of grease and oxides. In order to protect the metal surfaces from oxidation, they can be coated in the second washing step with a carrier, solvent and / or inhibitor, so-called surface protection.

Immediately after washing step c), soldering is carried out at a temperature of approximately 250 ° C with molten lead-tinale-20 jering in a known manner. Any residues left after watering are harmless.

Melting agent treatment, washing and surface protection can be done with a so-called crack wave. Figure 3 is a temperature curve illustrating the temperature changes during the different steps 25 a) -d). It can be seen from the figure that according to the invention '. the method provides a smoother and longer circuit preheating of the soldered surfaces of the plate (solid curve II) than the previously known method (dashed curve I). In the known method, a "temperature peak" is formed due to soldering and washing in the last step, which results in a more abrupt change in temperature than in the method according to the invention. This is, of course, a disadvantage due to the risk of mechanical damage (breakage, cold soldering). The method according to the invention causes a slower heating of the solder material and cooling of the S9 665. It is therefore necessary that the temperature is high enough in the washing step according to Figure 2c) so that a constant heating is maintained.

Claims (5)

5 S 9 6 c 5 A method for removing organic and inorganic residues from an object, for example a circuit board, which is to be soldered, which method comprises melt treatment, heating and washing, characterized in that the method is carried out in the following successive steps: a) melt treatment by itself (b) heating to a certain temperature higher than the temperature during the melt treatment to activate said surface; (c) washing the surface with water at a temperature approximately equal to that at the heating stage; and d) soldering performed immediately after said washing. Method according to Claim 1, characterized in that the surfaces to be soldered are coated during the washing step c) with surface protection to protect the surfaces from oxidation. A method according to claim 1 or 2, characterized in that if the soldering is performed at a temperature of 250 ° C, heating is performed in said heating step to approximately 100 ° C and subsequent washing. is made with water at a temperature of 70-80 ° C. A method according to claims 2 and 3, characterized in that the washing is performed in two steps with water at approximately the same temperature, said coating with a surface protection agent being performed in a later washing step. 8 9 6 8 S