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Research on the cause of IC mark failure



With the application of integrated circuit electronic products becoming more and more common, the natural environment it faces becomes quite complex, which will increase the failure probability of electronic components. When the failed components are ready to be replaced or found problems, the name and model of integrated circuit components will become a very important identification mark, so the quality of device printing marks will also be related to The stability of electronic products and even the whole system. In all kinds of complex climate conditions, to ensure the integrity of printed marks has become a problem that must be paid attention to.           

1.       Test and results           

There are two printing methods for devices: laser printing and ink printing: ink printing is to print the device's mark on the shell with glass ink (or silver compound, etc.), laser printing is to print the device's mark on the ceramic shell with laser machine. Although the laser printed handwriting is permanent, because the laser printed handwriting is not bright enough, there is no ink printing It's easy to recognize, and laser printing requires special equipment. Because of the high cost, there are many marks of devices printed with ink on the ceramic shell. According to the climatic conditions when the device is used, we choose the alternating humidity heat test, salt spray test and solvent resistance test to test the device, so as to understand and improve the stability and firmness of the device marks under these test conditions.          

1.1   experimental methods and conditions [1]           

Alternative damp heat test: certain conditions: cycle times: 10 times, 24 hours each time.           

Salt spray test: salt concentration: 2.0%; temperature: 35 , time: 24h; deposition rate: 30000mg / m2 / 24h.           

Solvent resistance test: temperature: 65 - 70 ; 42 volumes of deionized water, 1 volume of mixture of ether and 1 volume of ethanolamine; immersion time of device: 2min, brush forward 10 times.           

We selected 60 ink printing devices and 60 laser printing devices, and divided them into three groups on average. According to the above conditions, we carried out the alternating humidity and heat test. See Table 1 for salt spray test and solvent resistance test.           

1.2 failure phenomenon           

1.2.1 solvent resistance test           

Among the devices printed with ink, most of the marks of two devices fell off. The marks of one device are unclear, and none of the three devices can be identified; the marks of 20 devices printed by laser can be clearly identified.           

1.2.2 alternating damp heat test           

The marks of 20 devices printed by ink and 20 devices printed by laser can be clearly identified.         

1.2.3 salt spray test           

For ink printing devices, most of the six marks fell off and there were corrosion spots. A small part of two marks fell off, which was difficult to identify. One mark existed as a whole, but it was unclear. For laser printed devices, seven marks were incomplete due to the corrosion of the cover plate.

2.Failure mechanism and analysis of 2 devices           

Ink printing is to print on the cover plate with ink as a mark, and then bake at high temperature for a certain period of time to make the ink solidify on the cover plate as a mark for device identification. Laser printing is to print on the cover plate of the device through the laser beam. The depth of laser printing on the cover plate is less than the thickness of the protective metal coating on its surface, and will not damage the surface of the device The failure phenomenon is analyzed based on several test mechanisms.           

2.1 solvent resistance test           

Solvent resistance test is to put the chemical reagent into the container at a certain temperature, and then immerse the device in the container for a period of time (the chemical solution should cover the whole device). Wipe the mark on the surface of the device with a tool as required to see if there is any failure.          

In the test, three devices printed by ink failed to mark because the test reagent was organic solvent and ink was also composed of organic substances. When the device was immersed in the corresponding solution and temperature, the ink either did not cure well, or there was some contamination or impurity between the ink and the cover plate due to unclean surface of the cover plate. When there was external force or When the solution acts, the mark will move or fall off due to its unsteadiness or chemical reaction. Because the organic solvent generally can not dissolve the metal substance, and the laser printing is carried out on the metal surface, without organic components, so the chemical reagent can not change the mark of the stimulated light printing device, that is to say, the solvent resistance test is not suitable for laser printing It will have an impact.           

2.2 alternating damp heat test           

The test is to place the device under a certain temperature and humidity, so that the device can bear the change of temperature and humidity. When the temperature in the test equipment is lower than that of the device, condensation will occur. If the printing mark is not firm, it will be diluted or even fall off due to the disappearance of condensation. In the test, water molecules will permeate due to the change of temperature and humidity. At this time, if the temperature is lower than that of the device, condensation will occur. If the printing mark is not firm, water molecules will permeate When printing marks are not firm or there are many impurities on the surface of the cover plate, the water molecular connection is easy to penetrate between the marks and the cover plate, resulting in the failure of the marks.           

The devices printed by this group of inks did not lose their marks due to their firm printing or less impurities between the ink and the cover plate. Because the handwriting of laser printed devices is difficult to erase, no devices failed to mark.           

Because the experimental conditions of alternating humidity and heat experiment have little effect on the device labeling, the effect of this experiment on the labeling is much smaller than that of solvent resistance experiment and salt spray experiment.           

2.3 salt spray test           

The test is to place the device in the device at a certain angle and make the device accept a certain concentration at a certain temperature. This method is cruel and destructive to the device.           

In the experiment, 9 marks of ink printing device failed, and 7 marks of laser printing device also failed, which we analyzed.           

The main components of the device surface cover plate are Ni Fe, and Ni and Au are plated on the outside. When low-level metal is exposed on the surface of the cover plate, Ni Au and Fe Au primary batteries will be formed in the electrolyte (salt solution), and chemical reactions will take place. The specific reaction mode is as follows [2]:            

That is, Fe (OH) 2 and Ni (OH) 2 are formed. At this time, Cl - ions in the electrolyte will also participate in the reaction, and the following reactions will take place:           

Make the Ni and Fe on the cover plate dissolve continuously, forming corrosion. The marks of 6 devices printed by ink and 9 devices printed by laser are not well treated on the surface of cover plate, and there are various impurities or scratches on the surface. In addition, due to the destructive effect of Cl - ion, the coating breaks, exposing the metal inside, generating electrochemical reaction, and generating corrosion points on the surface of cover plate. When the corrosion point affects the mark, the mark will break and fall off.           

However, for the devices with the cover plate surface treated, the metal does not participate in the chemical reaction, and the mark will not fall off due to the cover plate failure. However, due to the strong penetrability of Cl - ion, it will pass through the ink and reach the cover plate. In this process, the ink with poor curing or quality problems will become soft, and the ink will slide down, which will lead to the mark failure.

3.Several factors affecting device marks           

Through the above analysis, we can get several factors that affect the marker.           

3.1 unstable curing           

The reason is that there are some contamination or impurities between the mark and the cover plate due to the unclean cleaning of the surface of the cover plate when printing ink, or the baking time is not long enough when the ink is solidified. The temperature is not high enough, so the mark can not be fixed on the cover plate of the device stably after curing. After some tests related to the mark, it is easy to make the mark fall off and so on.           

3.2 ink problems           

The ink quality is not good or its application is uneven, which is easy to cause uneven solidification of each part of the ink during curing, resulting in poor local corrosion resistance, thus affecting the whole mark, and even leading to complete falling off of the mark.           

3.3 plating of cover plate           

Because of the scratch on the surface of the cover plate, the low-level metal will be exposed and the corrosion will occur due to the chemical reaction; or because of the poor quality of the coating, the conditions for forming the primary battery will be formed, which is also the reason for the falling off of the mark on the surface of the sample during the mark test.           

4. Conclusion          

 Although the mark can not affect the electrical performance of the device, it is also an important part of the device. It is also an important process to keep the mark stable. Therefore, when printing, it is necessary to ensure the quality of the ink used is stable. Reliable; when coating, the force should be lighter and keep stable. The cover plate surface of the device should be cleaned without large impurities or particles. The metal coating should not have scratch signs.

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