PCB Technical - PCB problem Can the expired AB glue Epoxy be saved in addition to being scrapped?

What should you do if your AB glue epoxy resin (Epoxy) expires (exceeds the shelf life)? scrapped? Still use it?Many people think that it seems a pity that Epoxy is scrapped after it expires.What problems will there be if you continue to use expired Epoxy without scrapping it?

The use of expired Epoxy may basically cause two major problems such as failure to fully cure and decrease in surface resistivity (SIR) or volume resistivity (Volume Resistivity).

I believe most of my friends can understand the problem that Epoxy cannot be cured,because Epoxy will salivate to the outside of the product and cause cosmetic problems. In addition, it will also lose the protection purpose of Epoxy dispensing/pouring. However, the other "decrease in surface resistivity (SIR) or volume resistivity" is not so easy to understand, but we can first talk about the impact of the decrease in resistivity. The biggest problem is the leakage current.If the problem is light, it may increase the power consumption of the product and reduce the battery life. If it is serious, it may even cause unstable operation of the product, resulting in the risk of crash or restart.

How can we ensure that the expired Epoxy can still be used?

Our approach is to distinguish Epoxy’s Date-code first, and then take an empty circuit board to find two independent solder pads (pads) with a distance of 0.1mm. It is recommended to measure whether there is impedance first, and connect the surroundings.The trace is cut, and then a wire is welded on it to facilitate subsequent impedance measurement. Finally, the expired Epoxy glue is applied on it. Epoxy must cover all solder pads,and then follow the normal curing procedure Operation,not only can test whether Epoxy can be completely cured, but also measure its resistivity,whether it is suitable for your company's product requirements.

The minimum distance between the two solder pads is recommended to refer to the actual situation of the respective company,and be sure to find the minimum distance between the solder pads covered by Epoxy. As for whether the flux after soldering should be cleaned, it is recommended to make a set of clean and unclean.The flux is cleaned The impedance of the pure Epoxy can be measured, and the worst case is simulated SMT or repaired if it has not been cleaned. As for how much the measured impedance must be greater than, our company’s regulation is 1*108 ohms or more. It is recommended to consult their respective RDs to see if your company's product design has higher impedance requirements.

Finally, let's talk about why the expired Epoxy will cause the above problems?

The following are just personal opinions. The answer may not be correct and is for reference only. If you have an Epoxy expert, please jump out and help correct the error.

Epoxy will produce sediments after a long period of time. This is because the content of Epoxy will contain many macromolecular chemical components, and some will be doped with a small amount of metal components. These heavier chemical components will follow The influence of time and gravity slowly settles under the liquid Epoxy. If the deposit is too much, it will even harden locally. Therefore, the early barreled Epoxy will require the tube to be stored upside down when it is stored. It must be placed on a drum machine or a vibrating shaker and shaken for more than 10 minutes. The purpose is to evenly distribute these sediments into the Epoxy liquid.

If you still find hardened deposits after the above-mentioned shaking or rolling, be careful not to use this can of glue. If it is really necessary, you must crush the hardened deposits to dissolve it. In the original Epoxy liquid, otherwise there is a great chance of incomplete curing products.

If you have to use these expired AB glue Epoxy, is there a way to verify its quality?

Our approach is to first select AB glues of different Date-codes according to the date. For each type, first choose a can to test the glue. The key points of the judgment are two:

Check if Epoxy has cured completely. The glue that has been filled should be cut open for inspection.

Choose two solder pads with a distance of 0.1mm on the circuit board, each solder pad is connected with a wire, and then add Epoxy on it until it completely covers the two solder pads and solder joints, wait until the Epoxy is cured, use "High resistance meter" measures the insulation resistance value. Our requirement is that it must be greater than 100M ohm. Of course it depends on the design of each product.

If the above two items are all positive, then fill the glue slowly one by one. In order to ensure that the glue will really be completely cured, you must make and keep a record of the dummy epoxy for each glue to check the glue. The quality of curing. In addition, the production line can also be required to place the cured product upside down in the process. At this time, if there is an incompletely cured product, Epoxy will flow out, which can be visually checked, so that the production line of the circuit board manufacturer can intercept To the defective product, instead of waiting for the customer to complain when they receive it.