Suggestions on solder improvement

1. Poor tin dipping: This is an unacceptable defect, and only some solder joints are stained with tin. The reasons and improvement methods are analyzed as follows:

1- 1. External pollutants, such as oil, grease and wax. Generally, it can be cleaned with solvent, and this kind of oil stain is sometimes touched when printing solder resist.

1-2. Silicone oil is usually used for demoulding and lubrication, and usually appears on the bottom plate and parts feet. Silicone oil is not easy to clean, so be very careful when using it, especially when it is used as antioxidant oil, it will volatilize on the substrate, resulting in poor tin staining.

1-3. Due to poor storage conditions or problems in substrate manufacturing, oxidation often occurs. When the flux cannot be removed, it will lead to poor tin coloring. Secondary tin plating may solve this problem.

1-4. The way of flux is incorrect. This is because the foam pressure is unstable or insufficient, which leads to the high instability or unevenness of foam, so that the substrate part does not contact flux.

1-5. Insufficient tin eating time or tin temperature will lead to poor tin dipping, because molten tin needs enough temperature and time to be wet. Usually, the soldering temperature is 50℃ to 80℃ higher than the melting point temperature, and the total tin immersion time is about 3 seconds. 2. Poor local tin immersion DE WETTING: This situation is similar to poor tin immersion, except that poor local tin immersion will not expose the surface of copper foil. Only a thin layer of tin cannot form a complete solder joint. 3. Cold welding or solder joint is not bright. Cold welding or far solder joint: the solder joint seems to be broken and uneven, mostly because the parts vibrate when the solder is about to cool to form the solder joint. Pay attention to whether there is abnormal vibration in tin furnace transportation. 4. Solder corner crack: This situation is usually caused by the mismatch of expansion coefficients of solder, substrate, through holes and parts feet, and should be improved in substrate materials, parts materials and design. 5. Too much tin in the solder joint: A solder joint is usually evaluated, and it is hoped that the solder joint will be big, round and fat. However, in fact, too large a solder joint may not be helpful for conductivity and tensile strength. 5- 1. Incorrect conveying angle of tin furnace will lead to excessive solder joints, and the inclination angle will be adjusted from 1 to 7 degrees according to the design method of the substrate. Generally, the angle is about 3.5 degrees. The greater the angle, the thinner the immersion angle and the thicker the immersion angle.

5-2. Increase the temperature of the tin bath and prolong the welding time, so that the excess tin can flow back into the tin bath.

5-3. Increasing the preheating temperature can reduce the heat required for tin plating on the substrate, thus improving the welding effect.

5-4. Change the specific gravity of flux, and slightly reduce the specific gravity of flux. Generally, the higher the specific gravity, the thicker the tin will be and the easier it will be short-circuited. The lower the specific gravity, the thinner the tin is, but the easier it is to cause tin bridges and tin tips. 6. icicle of tin tip: This problem usually occurs in the welding process of DIP or WIVE, and tin similar to ice tip is found at the top of the part foot or at the solder joint. 6- 1.

6-2. The area of gold wires (pads) on the substrate is too large, which can be improved by separating the gold wires with green (solder-proof) paint wires. In principle, the green (solder-proof) paint line is used to divide the gold track surface into 5 mm× 10 mm blocks.

6-3. The temperature of the tin bath is insufficient and the tin dipping time is too short. It can be improved by increasing the temperature of the tin bath and prolonging the welding time, so that excess tin can flow back into the tin bath.

6-4. The cooling air flow angle after the peak is wrong, so it is not allowed to blow in the direction of the tin bath, which will cause the tin spot to be rapid, and the excess solder cannot be pulled back to the tin bath by gravity and cohesion.

6-5. Tin tips are produced during manual welding, usually because the soldering iron temperature is too low, so that the soldering tin temperature is not enough to form solder joints immediately due to cohesion retraction. Use a soldering iron with a large wattage to prolong the preheating time of the soldering iron on the welded object. 7. Solder tape: 7- 1. When manufacturing the substrate, some substances are incompatible with the flux. After post-etching, sticky solders stick together to form tin wires, which can be cleaned with solvents such as acetone (* a chemical solvent that has been banned by Montreal Convention) and chlorinated olefins. If it can't be improved after cleaning, it may be that the substrate is cured incorrectly. The accident shall be reported to the substrate supplier in time.

7-2. Incorrect substrate curing will cause this phenomenon, so it can be baked at 120℃ for two hours before the plug-in, and this accident should be reported to the substrate supplier in time.

7-3. Tin slag is pumped into the tin bath by a pump, and then sprayed out, resulting in tin slag on the surface of the substrate. This problem is relatively simple and good tin furnace maintenance, and the correct height of the tin surface in the tin bath (generally, the height of the tin surface from the edge of the tin bath when the tin bath is not sprayed is 10mm). 8. White residue: White residue, usually rosin residue, is found on the substrate after welding or solvent cleaning. This substance will not affect the surface resistance, but the customer does not accept .8-1. Flux is usually the main cause of this problem, and sometimes it can be improved by switching to another flux. Rosin flux often shifts in the cleaning process. At this time, the best way is to seek the assistance of flux suppliers whose products are more professional.

8-2. Impurities left over from the substrate manufacturing process will also produce white spots after long-term storage, which can be cleaned with flux or solvent.

8-3. Incorrect curing can also lead to white shift, which is usually produced separately in a batch. Report to the substrate supplier in time and clean it with flux or solvent.

8-4. When replacing a new substrate supplier or a brand of flux, the flux used in the factory is incompatible with the oxide protective layer of the substrate, and the supplier's help should be sought.

8-5. Because the solvent used in the substrate process will change the substrate material, especially the solution in the nickel plating process will often cause this problem, it is suggested that the shorter the storage time, the better.

8-6. The flux will age after a long time of use, and will deteriorate after being exposed to air to absorb moisture. It is recommended to update the flux (usually foaming flux is updated once a week, soaking flux is updated once every two weeks, and spraying flux is updated once a month).

8-7. Use rosin-based flux, wait in the welding furnace for nine minutes and then clean it, resulting in white shift. Shorten welding and cleaning time as much as possible to improve it.

8-8. The water content of the solvent used to clean the substrate is too high, which will reduce the cleaning ability and produce day shift. The solvent should be updated. 9. Dark residue and etching trace: Usually, black residue appears at the bottom or top of solder joint, which is usually caused by improper use of flux or improper cleaning. 9- 1. Rosin flux is not cleaned immediately after welding, leaving dark brown residue, so try to advance it as soon as possible.

9-2. The acid flux remaining on the solder joint will lead to black corrosion and cannot be cleaned. This phenomenon often occurs in hand welding, so it is necessary to clean it with weak flux as soon as possible.

9-3. Organic flux burns at a high temperature, resulting in black spots. Confirm the temperature of the tin bath and use high temperature resistant flux. 10. Green residue: Green is usually caused by corrosion, especially electronic products, but not completely, because it is difficult to tell whether it is green rust or other chemical products, but generally speaking, the discovery of green substances is a warning, and the reasons must be found out immediately. In particular, this kind of green substance will become bigger and bigger, so we should pay great attention to it. Generally, it can be improved by cleaning. Corrosion problems usually occur on bare copper surfaces or copper-containing alloys. When using non-rosin flux, this corrosive substance contains copper ions, so it is green. When this green corrosive substance is found, it can be proved that the cleaning after using non-rosin flux is incorrect.

10-2. Copper rosin acid is a compound of copper oxide and rosin acid (the main component of rosin). This substance is green, but it is by no means corrosive and has high insulation, which will not affect the quality, but the customer will not agree to clean it.

10-3. Pre-sulfate residues or similar residues in substrate manufacturing will produce green residues after welding. The substrate manufacturer shall be required to conduct cleanliness test after the substrate is manufactured and cleaned to ensure the quality of substrate cleanliness. 1 1. The eighth white corrosion refers to the white residue on the substrate. This project is about the white corrosion of parts and metals, especially for metals with more lead components, mainly chloride ions are easy to form lead chloride with lead, and then form lead carbonate with carbon dioxide (white corrosion). When using rosin flux, because rosin is insoluble in water, chlorine-containing activator will not be corroded, but if the solvent used is improper, chloride ions can only be removed by washing rosin. This will accelerate corrosion. 12. Pinholes and blowholes: The difference between pinholes and blowholes is that pinholes are small holes found on solder joints, while blowholes are large holes on solder joints where the inside can be seen. The interior of pinhole is usually empty, while the air hole is a big hole caused by the complete ejection of internal air, which is caused by the solidification of solder before the gas is completely removed. This problem arises. 12- 1. Organic pollutants: Both the base plate and the parts feet may generate gas, which may lead to pinholes or air holes. Pollution sources may come from automatic seeders or poor storage conditions. This problem is relatively simple, just wash it with solvent. However, if it is found that the pollutant is SILICONOIL, other substitutes should be considered in the process.

12-2. There is moisture in the substrate: if cheaper substrate materials are used or rough drilling is adopted, moisture is easily absorbed at the through hole, which is caused by high heat evaporation during welding. The solution is to bake in an oven at 120℃ for two hours.

12-3. Brightener in electroplating solution: When a large number of brighteners are used for electroplating, the brighteners often precipitate gold at the same time, which is caused by volatilization at high temperature. Especially when gilding, electroplating solution containing less brightener is used, and of course this should be fed back to the supplier. 13. trapped oil: oxidation prevention oil is pumped into the tin bath and sprayed out to pollute the substrate. This question should be tin.

(1) After welding, the color of the solder joint will turn dark for a period of time (about six months to one year).

(2) The finished solder joint is gloomy. 14- 1. Impurities in solder: The metal composition in solder must be checked regularly every three months.

14-2. Flux will also produce a certain degree of gray on the hot surface. For example, RA and organic acid flux will cause slight corrosion and turn gray if left on the solder joint for a long time, and should be cleaned immediately after welding to improve it. Some inorganic acid fluxes will cause zinc oxychloride to be washed with 1% hydrochloric acid first, and then with water.

14-3. In solder alloys, solder joints with low tin content (such as 40/60 solder) are also dark. 15. The surface of solder joint is rough: the surface of solder joint protrudes from the surface like sand, but the overall shape of solder joint remains unchanged. 15- 1. crystallization of metal impurities: it must be done regularly every three months.

15-2. Tin slag: Tin slag is pumped into the tin bath by a pump and then sprayed out by a nozzle. Because tin contains tin slag, there is a sand-like protrusion on the surface of the solder joint, which should be because the solder level in the tin bath is too low. Adding solder to the tin bath can be improved by cleaning the tin bath and pump.

15-3. Foreign bodies such as burrs and insulating materials are hidden in the feet of parts, and rough surfaces can also be produced. 16. Yellowing of solder joint: It is caused by too high solder temperature. Check whether the solder temperature and thermostat are faulty immediately. 17. Short-circuit bridging: Two solder joints are connected due to too large solder joints. 17-.

17-2. Poor flux: improper flux ratio, deterioration, etc.

17-3. The direction of the substrate does not match the tin wave, which changes the tin eating direction.

17-4. Bad line design: lines or contacts are too close (spacing should be greater than 0.6 mm); If it is an array solder joint or IC, you should consider stealing soldering or separating it with text white paint. At this time, the thickness of white paint should be more than twice that of pad (gold wire).

17-5. The polluted tin or excessive oxide is short-circuited by the pump belt, so the tin furnace should be cleaned or the solder in the tin bath should be completely updated.