Why does solder paste need to be cleaned? What is the incorrect cleaning operation?

The no-clean solder paste meter is used nowadaysSMTIn the production process, it is widely used in the repair operations of mobile phone and computer board cards, and can also be usedBGAFor the production operations of other electronic components, a low-ionic activator system with high reliability is adopted, which leaves very little residue after soldering and has a relatively high insulation resistance. Even without cleaning, it can still have extremely high reliability. In addition, no-wash solder paste can be provided in various packaging methods, such as bottle type, syringe type, etc., to meet the requirements of different products and processes of customers. Solder paste is usually best stored in the refrigerator at a temperature of5-10℃It's best. Therefore, when taking the solder paste out of the cold box, its temperature is much lower than the room temperature. If the bottle cap is opened without "warming up", it is easy for the water vapor in the air to condense and adhere to the solder paste, and during the welding process (usually when the temperature exceeds200℃The moisture rapidly vaporizes due to intense heat, causing a "splashing" phenomenon, generating tin beads and even damaging components. Warming method: Without opening the bottle cap, place it at room temperature to thaw naturally and warm up4About an hour. When warming up, be careful not to open the bottle cap without sufficient warming up. Do not shorten the "warming up" time by heating. Now, JJY solder Paste Manufacturer will explain it to you:

Flux pasteWhy clean:

After the soldering flux is welded, there will be some residue to a certain extent, and the residues can be classified into several types:

Particulate pollutants are prone to cause electrical short circuits.

Polar contaminants can cause dielectric breakdown, leakage and corrosion of component circuits, etc.

Non-polar contaminants can affect the appearance, mainly due to white powder, adhered dust, and poor electrical contact.

Incorrect understanding of cleaning:

In order to meet the requirements of electronic manufacturers, solder paste manufacturers have launched no-clean solder paste, although it is indicated in their product manualsRAWords. However, in many occasions with high precision requirements, such as military and aircraft components, even those with relatively weak activityRMAThe type of flux paste also needs to be cleaned to ensure reliability. whileRASolder paste, due to its strong activity, also brings problems such as corrosion and leakage. Unless it is applied in low-demand markets like fans, it must be cleaned and is limited by existing detection methods.RAThe solder paste may be very high during the inspectionSIRHowever, problems such as image streaks and tone distortion caused by leakage of electricity still occur during use, which has been confirmed by many manufacturers.

Incorrect cleaning operation:

AWhen ultrasonic waves are not available, simply soak the circuit board and then take it out to dry.

BUse a brush dipped in cleaning agent to scrub the circuit board a few times.

As introduced earlier, the residual components of solder paste are complex and difficult to clean. It is not something that can be washed off casually. Otherwise, there is no need to use ultrasonic cleaning.

In the flux paste residue, non-polar contaminants mainly composed of rosin or other synthetic resins coat halogens, organic acids, salts, etc., playing a "plastic sealing" role. This significantly reduces the corrosion caused by ionic contaminants and avoids problems such as leakage after moisture absorption. During the cleaning process, resin is the first to be washed away. If the cleaning operation is stopped at this time, what remains on the circuit board will be ionic contaminants, and the consequences can be imagined. The problems caused by incomplete cleaning are far more serious than those of no cleaning at all. Therefore, once cleaning is carried out, it must be done thoroughly.

How to improve the cleaning effect;

AIt should be cleaned as soon as possible after welding(1Within one hour);

BIncrease the preheating temperature of the cleaning agent;

CExtend the cleaning time;

DReplace the cleaning agent frequently with new ones.

Inspection after cleaning

AVisual estimation: For use2～10Use a double optical microscope to inspect the circuit board for solder paste residues and other contaminants. This method is relatively simple, but it is very difficult to quantitatively represent trace residues.

BSolvent extraction: Immerse the circuit board in the test solution and then measure its ionic conductivity.

CMeasure the surface insulation resistance(SIR).

If you want to master the difficult problems related to soldering methods such as flux paste, lead-free solder paste, and solder paste, we warmly welcome you to consult Shenzhen JJY Industrial Production High-tech Co., LTD. Let's learn and grow together!