What is the Red Ink Experiment?
Put the solder joint in red ink or dye, let the red ink or dye penetrate into the crack of the solder joint, and forcibly separate the solder joint after drying, and the solder joint will generally crack from the weak link (crack).
Therefore, the red ink experiment can determine the size and depth of the crack and the interface of the crack by checking the staining area and interface of the crack interface, so as to obtain the quality information of the solder joint.
Sample Cutting:A wire cutting machine is used to cut the sample into a suitable specimen.
Cleaning:The sample was immersed in a container filled with isopropanol or toluene, cleaned in an ultrasonic cleaning machine for 5 minutes, and then dried by a heat gun after being removed.
Ink penetration:Pour ink in a suitable container until the specimen is submerged and place it in a vacuum chamber for 1-2 hours. Take care to place the device you want to observe face up.
Drying:Baking conditions: 85 12h, speed up the program 100 4h
Separation
Observe
Through cross-section dyeing analysis, the state and cause of failure can be determined, and the main failure modes are divided into the following types:
1. BGA pillow effect phenomenon:The BGA side and the PCB pad side are stained and dimple-shaped.
2. Overall dyeing of the section:
The PCB side pad and BGA solder joint section are stained, but the section is in a smooth state, and the reason is:
1) BGA is deformed by external stress, and the solder joint fractures;
2) Poor BGA repair.
No ink infiltration after separation
1) The pads on the P board are pulled out, and the substrate is not stained;
2) Separated from the welded section, it is silver-gray (IMC layer).
Sampling process:The test sample should be protected from being damaged by external mechanical stress. A special cutting and sampling machine should be used, and the cutting position should be kept at an appropriate distance from the device;
Cleaning:Before staining, special solvents are generally used to carefully clean the samples, and the cleaning agent is currently toluene or isopropanol;
Selection of staining solution:Choose a hydrophobic, dye-stable, permeable red ink. Avoid red ink absorbing moisture in the air, resulting in red or partially stained areas that do not have cracks, resulting in deviations in the results.
Device separation:
1) Ensure the dryness of the device and the necessary cleaning of excess materials;
2) Be careful not to push the device horizontally, and try to separate the device vertically to avoid the interface abrasion and unclear due to improper separation, which will affect the accuracy of the results.
Baking conditions:The temperature is generally controlled at about 100 °C, and the maximum is not more than 120 °C, so as not to exceed the TG temperature of the PCB and cause new failure modes.
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