What are the solderability test methods for SMT components?

Date：2021-10-13 17:02:47 Views：1393

Weldability refers to the difficulty of material welding operation, joint performance, and the weldability of electronic components. Oxidation or pollution is easy to occur on the welding end or pin surface of components. In order to ensure the welding reliability, attention must be paid to the packaging conditions and environmental conditions of components during transportation and storage. Measures should also be taken to prevent components from being exposed to the air for a long time before welding and to prevent them from being stored for a long time. Together, attention should be paid to the solderability test before welding, So as to find and deal with problems in time. There are many methods to detect the solderability of components. The following describes several commonly used methods.

1. What is SMT

SMT is the abbreviation of surface mount technology, which means Chinese mounting technology. SMT is a new generation of electronic assembly technology. Electronic assembly industry is the most popular technology and process at present. This will compress the traditional electronic components and equipment to only one of a few volumes.

2. SMT features

High assembly density, electronic information products have small volume and light weight. The volume and weight of patch components are only about 1 / 10 of that of traditional Chinese plug-in components. Generally, SMT can be adopted. After that, the product quality and volume of electronic enterprises continue to decrease by 40% ~ 60% and the weight by 60% ~ 80%. SMT products have high structural reliability and strong anti vibration ability; Low solder joint defect rate and good high frequency characteristics; Reduces an electromagnetic and RF signal interference. It is easy to manage, realize system automation and improve social production and operation efficiency. Reduce logistics costs by 30% ~ 50%. Save building materials, energy, equipment, manpower, time, etc.

3. Solderability test method of SMT components

1. Welding groove moistening method

The welding groove moistening method is one of the most original component solderability test methods. It is a test method evaluated by visual inspection (or magnifying glass). Its basic test procedure is: immerse the sample in the flux and take it out, remove the remaining flux and then immerse it in the molten solder groove about twice the actual production welding time, and then take it out for visual evaluation.

This test method is usually carried out by immersion tester. It can control the immersion depth, speed and residence time of samples according to regular parameters, so as to obtain the test results conveniently and quickly. This test method can only get a qualitative conclusion of visual measurement, which is not suitable for the test occasions with quantitative accuracy requirements, but it is more suitable for the fast and intuitive test requirements of SMT assembly production site, and it is still commonly used. The qualification criteria for solderability test by welding groove moistening method is that all samples to be tested shall show a continuous solder coverage, or at least more than 95% of the solder coverage of each sample is qualified.

2. Welding ball method

The weldability test of solder ball method is also a simple qualitative test method. Its basic principle is: select the solder ball of appropriate specification according to relevant standards and heat it on the heating head to a regular temperature; Place the parts to be tested (leads or pins) of the sample coated with flux horizontally and immerse them straight into the solder ball at a regular speed. Record the time until the lead is completely wet and completely wrapped by the solder ball. Measure the weldability by the length of this time. The evaluation criteria for solderability test by solder ball method are: the time when the lead is completely wet by solder ball is about 1s, and it is unqualified if it exceeds 2S.

3. Wet weighing method

The basic principle of the device and test principle for solderability test by wet weighing method is as follows: hang the component sample to be tested on the scale rod of the movable scale; Immerse the part of the sample to be tested into the melting welding at a constant temperature to a regular depth; Together with this, the resultant force of buoyancy and surface tension on the immersed sample in the straight direction is measured by the sensor and converted into a signal, and recorded into a force time function curve by a high-speed characteristic curve recorder; The function curve is compared with the ideal wet weighing curve obtained from an experimental sample with the same properties and size and can be completely wet, so as to obtain the test results.

Moisture balance tester is an instrument for weldability test by moisture weighing method. When the test sample is soaked with molten solder at a predetermined depth, at first, the solder liquid level is pressed downward into a meniscus shape, because the cohesion of the solder is greater than the adhesion between the molten solder and the test sample (PIN), so that the wet angle 8 is greater than 90 °, and the straight weight FR and buoyancy FB of the meniscus under the solder are in the same direction, so the test sample is evaluated upward. When the sample reaches the welding temperature, the adhesion between the sample and the molten solder is greater than the cohesion of the solder, and the molten solder begins to wet the sample, so that the meniscus gradually bends upward until 6 equals 90 °, and the test sample is only affected by buoyancy. Then, the molten solder is continuously wet, and the sample presents an upward meniscus, 9 is less than 90 °, and a downward tension effect occurs until the vertical weight fr of the surface tension FR is equal to the buoyancy FB, reaching the moisture balance.

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