Technology

How are aluminum electrolytic capacitors produced?

Compared with other capacitors such as film capacitors, tantalum capacitors, ceramic capacitors, etc., aluminum electrolytic capacitors have the advantages of large capacity, high withstand voltage, and high-cost performance, and become irreplaceable passive electronic components.

Aluminum electrolysis is the most common partner we encounter in PCBA processing, but do you know how it is produced and processed?

The main raw materials of aluminum electrolytic capacitors: anode foil, cathode foil, electrolytic paper, electrolyte, conductive foil, tape, cover plate, aluminum shell, washer, casing, gasket, etc.

Production process: cutting, winding, impregnation, assembly, aging, sealing, printing, casing, measurement, packaging, inspection, etc.

Aluminum electrolytic capacitor manufacturing process:

Step 1: Corrosion of aluminum foil

If you open the casing of an aluminum electrolyte capacitor, you will see several layers of aluminum foil and several layers of electrolytic paper inside. The aluminum foil and electrolytic paper are attached together and rolled into a cylindrical structure, so that every two layers of aluminum foil In the middle is a layer of electrolytic paper that absorbs the electrolyte.

Manufacturing essentials of aluminum foil. In order to increase the fighting area between the aluminum foil and the electrolyte, the appearance of the aluminum foil in the capacitor is not smooth, but through the electrochemical corrosion method, its appearance is formed into a rugged and unyielding shape, which may increase the appearance area by 7~8 times. The process of electrochemical corrosion is relatively complex, which involves the type and concentration of the corrosion solution, the appearance of the aluminum foil, the corrosion rate, the dynamic balance of the voltage, and so on.

Step 2: Oxide Film Formation Process

After the aluminum foil is galvanically corroded, it is necessary to use chemical methods to oxidize its appearance into aluminum oxide, which is the medium of aluminum electrolytic capacitors. After oxidation, carefully examine the appearance of aluminum oxide to see if there are freckles or cracks, and remove the unqualified ones.

Step 3: Cutting the Aluminum Foil

This measure is simple for you to understand. It is to cut a whole piece of aluminum foil into several small pieces to make it suitable for the needs of capacitor manufacturing.

Step 4: Riveting of the lead

The pins outside the capacitor are not directly connected to the inside of the capacitor, but are connected to the inside of the capacitor through the inner lead. Therefore, in this step, we need to properly connect the inner leads of the anode and the cathode with the outer leads of the capacitor through ultrasonic keys. The outer leads usually use copper-plated iron wires or oxidized copper wires to reduce resistance, while aluminum wires and aluminum foils directly connect the inner leads. The public pays attention to these small measures without fault. The precision processing requirements are very high.

Step 5: Winding of electrolytic paper

We can not directly pour the electrolyte into the capacitor, and soaks the aluminum foil in a liquid state, but pasted it with the aluminum foil layer by layer through the electrolytic paper that has absorbed the electrolyte. Among them, the formula of the selected electrolytic paper is somewhat different from that of ordinary paper. It is microporous, and the appearance of the paper is not as good as that of impurities. Otherwise, we will affect the composition and performance of the electrolyte. In this step, aluminum foil attached to the electrolytic paper that does not absorb the electrolyte and then rolled into the capacitor casing. So that the aluminum foil and the electrolytic paper form a partitioned state similar to “101010”.

Step 6: Impregnation of Electrolyte

After wounding the electrolytic paper, we can pour the electrolyte into it to immerse the electrolyte in the electrolytic paper. With innovation and improvement, we can gradually improve the current ESR value of aluminum electrolyte capacitors.

Step 7: Assembly

This step is to assemble the aluminum shell on the surface of the capacitor and connect the outer leads. At this time, we basically form the capacitor.

Step 8: Crimping

If it is the kind of “wrapped” capacitor, it is necessary to pass this step. That is to cover the PVC film on the surface of the aluminum shell of the capacitor. However, there are fewer and fewer capacitors using PVC film at present. Because this material is not suitable for the trend of environmental protection.

Step 9: Combination Assembly

Step 10: Charging and aging test

Aging is the last step in capacitor production. During this process, we will apply a DC voltage. Which is greater than the rated voltage but less than the forming voltage. Generally at the rated temperature of the capacitor. This process can repair oxide film defects. Aging is a good means of screening early failure capacitors. Low initial leakage current is a sign of effective aging.

Step 11: Parameter Review

We use the leakage test (Leakage Current up) to measure the capacitor plus the DC voltage. The voltage marked on the capacitor hose is the voltage. Capacitance review: the goal of the review is to test whether its value is within the allowable deviation range.

3DF review: Temperature 25°C frequency 120HZ, non-polarity usually 1KHZ (test conditions). A brief note: capacitors will naturally have a dissipation factor in the electronic circuit. Dissipation and loss are both bad in the Chinese word meaning. It uses the opposite side in the trigonometric function to find the value. DF is a common term in the Taixi region, and percentages express the edge and corner. The smaller the value, the better. We should discharge the capacitor before testing the capacity DF. So as not to damage the instrument due to the voltage of the capacitor itself flowing into (incoming) the instrument.

External review: that is, the aesthetics of the capacitor shape (beauty pageant), it must rely on our vision to judge whether it is good or not. In each of our manufacturing processes ahead, we all know what is good and when we should eliminate it. However, in order to prevent “fish slipping through the net”, some still need to review the outside.

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