Test method and specific steps of solderability of electronic components

Date：2021-09-22 15:14:08 Views：3514

There are many methods of electronic testing. Among them, solderability test refers to the qualitative and quantitative evaluation of the solderability of components, PCB, pad, solder and flux through the principle of wetting balance method. It is of great help to the level 1 (IC packaging) and level 2 (electronic components assembled to printed circuit board) processes of modern electronic industry, which need high-quality interconnection technology and high-quality and zero defect welding process. Solderability of components refers to their ability to be welded within a specified time and at a specified temperature. It is related to the thermal characteristics, wettability and heat resistance of components. For example, optical fiber socket is difficult to weld by hand because of its large heat capacity. Let's take a look at the test methods and specific steps of solderability of electronic components.

Immersion welding test

Immersion welding is the simplest method to test the solderability of the lead or welding end of components. It is to immerse the lead or welding end into the molten solder groove and take it out to observe its wetting degree by visual inspection.

Immersion welding test procedure

1. Temperature rise

Heat the solder in the welding groove and keep it at the required temperature.

Lead containing process: 63Sn37Pb, 235 ℃

Lead free process: 95.5sn3 9Ag0. 6Cu，255℃

2. Dip coating flux

First, install the test sample on the fixture, then immerse the surface to be tested in (room temperature) flux for 5S, and finally take it out and drip dry (stay in air for 5 ~ 20s).

Axial, radial or multi pin leads installed through holes shall be vertically inserted into the flux slot; The surface solderable end of surface mounted components shall be immersed at an angle of 20 ° ~ 45 ° with the flux liquid level, and the immersion depth shall be about 1.27mm away from the component body.

3. Solder dipping

The oxide and scum on the solder surface shall be removed before each solder dip.

The through-hole plug-in components shall be immersed in solder, and the immersion and disengagement speed shall be 25.0mm/s ± 6.0mm/s; The dwell time is 5.0s ± 0.5s.

For components with pins attached to the surface, immerse the sample at 20 ° ~ 45 ° or 90 ° with the liquid level of flux or solder.

The depth of surface mounted non pin components shall be controlled within 0.1mm. The immersion and detachment speed is 25.0mm/s ± 6.0mm/s, and the residence time is 5.0s ± 0.5s. The residence time of large components can be slightly extended.

Immersion welding test

Check the surface wetting of the test sample with a 10x magnifying glass under appropriate light conditions and accept it according to j-std-002.

Wetting weighing test

Quantitatively test the wettability of the component lead or welding end. The tested component is suspended on the dynamometer on the molten solder pot. When the solder groove rises and the component welding end is immersed in the solder, firstly, the temperature of the welding end is too low to be wetted. The component arranges the solder, receives upward buoyancy on the meter, the welding end is wetted, and the surface tension pulls the component down into the pot, The dynamic stress curve can be used to represent the weldability of the welding end. This dynamic stress curve is called the wetting curve.

Wet weighing test procedure

1. Sample preparation:Before the test, the lead or welding end shall not be cleaned or scratched, and it shall be ensured that it is not polluted by fingerprints.

2. Flux coating:Immerse the component lead or welding end in the flux for a few seconds and drip dry.

3. Immersion test:The entry rate of chip components is 1mm / s, and that of lead components is 5mm / s.

Wet weighing acceptance criteria

When the wetting time is within 2S, the wetting force remains positive; There is no discontinuity or change of direction in the slope of wetting force curve measured after 1s; The wetting force after 3S is at least 25% of the wetting force of the best wetting standard element.

Precautions for solderability test

The solderability test must use the specified flux, solder, cleaning agent and pre-test aging treatment

flux

Inactive R-type flux is recommended for testing incoming components. Requirements for main components:

Water white rosin 25% (wt%);

Isopropanol, purity 99%;

Density, 0843g / cm3 ± 0.005g/cm3 (25 ℃).

For on-line production test, RMA or RA flux can be used, which can accurately reflect the actual production situation.

solder

Lead element test, 63Sn37Pb (wt%);

Lead free component test, 95.5sn3 9Ag0. 6Cu（wt%）。

Cleaning agent

Isopropanol, purity 99.5%.

Samples must be taken at random

The sample must be steam aged

The leads or welding ends of components show high solderability when they are just produced, but their solderability will deteriorate after the components are stored for a period of time. The reason is that the components will be oxidized and eroded when exposed to the air. Therefore, the solderability test must consider the impact on the performance of components under normal storage conditions.

According to the fact that components and PCBs generally have a storage cycle of 6 ~ 12 months before assembly, aging treatment must be carried out before solderability test - the common method is dry heat aging or steam aging, so as to reflect the actual solderability. Generally, for the decrease of weldability mainly caused by diffusion, the dry heat aging method of 115 ℃ and 4H is adopted; For the decrease of weldability with unclear mechanism, 8h steam aging method shall be adopted.

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