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PCBA reliability should start from the bottom
2021-09-27
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Author:Frank

PCBA reliability should start from the bottom
Establishing a reflow temperature curve for electronic components is like trying to calculate the time and temperature used to bake turkey, chicken, and lobster (baking temperature curve), using the same time and temperature in the same baking oven Roasting turkey, chicken and shrimp will not fail to cook the turkey, nor will the shrimp be battered. However, the difference between the two is that for electronic products, the consequences of using a poor reflux temperature curve are far more disappointing than the disappointment of the guests who come to eat because the turkey is not cooked or the shrimp is overroasted.

Simply put, before the product is put into actual use, the cost of special reliability testing of the product will be much cheaper. If the problem is discovered after the product is released, you must find the problem through backtracking, and determine whether everything that occurs in the field application has the risk of causing the product to malfunction and be recalled. Then, you must also look back. Do the tests that you should have done in the beginning. If you consider repairing or replacing the product, even if you do not consider other costs related to the recall, such as the possibility of continuing future business cooperation with the customer, the cost of the recall may be much higher than the original value of the project itself. For your product, the most important factor may be related to certain things that determine human life.

From all aspects, the impact is very bad. The most typical example of a product recall is the airbag incident of Japan's Takata Corporation. Although the incident is not directly related to the situation in our electronic hardware field, this example illustrates that extensive reliability testing must be carried out before the product is released. The biggest loss related to the recall is casualties, but from a commercial point of view, Takata lost more than 24 billion U.S. dollars in this recall, and eventually led to the company's bankruptcy. If the PCBA used to control the pizza oven is broken, the risk It is much lower (this problem is open to discussion), but the most likely problems can be eliminated by appropriate reliability tests in the front.

pcb board

I plan to share with you some test suggestions based on failure analysis, as well as the experience and lessons learned from some of our customers through case analysis and failure unit data over the years. There is no doubt that I will be very concerned about cleanliness and the relationship between it and reliability.

What does reliability mean? According to the explanation of the Almighty Internet, reliability refers to "the quality is trustworthy or its performance is good from beginning to end." In my opinion, whether a product is reliable, like from a height of 50,000 feet Looking down at the products being manufactured on the ground, this is the summary of reliability. As we get closer to the ground, we need to analyze it more specifically and classify it into the category of products to be produced. In the large vem quality chart, the reliability problems of category 1 electronic products are not big; they are likely to work normally after they leave the factory. In many cases this is the case.

When looking at Type 2 and Type 3 hardware, the most important issue to be concerned about is definitely reliability. According to IPCA610, "Class 2 dedicated service electronic products include products that require continuous work and long life, as well as products that require uninterrupted service but are not critical services. Under normal circumstances, the end-use environment will not cause product failure." "Category 3 high-performance electronic products include the ability to work continuously with high performance or work on demand. This is crucial. The equipment is not allowed to stop. The end-use environment may be extremely harsh. As long as there is a need, the equipment must operate, such as life Maintain the system or other critical systems.

This tells me that not all electronic products have the same reliability. In the final analysis, the reliability requirements of these two types of electronic products have some subtle differences. Except for some high-end unique components, most parts and assembly processes can meet the requirements of these two types of products. The biggest difference between these two types of products is what happens if the product fails. In some cases, this is actually a matter of life and death. It is very important to remember this. The good news is that most companies that produce this type of electronic products are very sure about the reliability of their products, and many Type 2 electronic components do not need to do these tests.

There is enough discussion about the speciousness of electronic products. Let's start with reliability issues. Because you need to know that blank circuit boards and components are stable, and will bring you some surprises within a period of time, approving new suppliers for the parts used in your process is the key to achieving product reliability. Let's start with a blank circuit board. When you start discussing the guidelines, any agreement reached between the user and the supplier will dominate the demand from other sources.

Most companies use "IPC6012: Qualification and Performance Specifications for Rigid Printed Circuit Boards" instead of internal guidelines. When we are investigating the applicable documents specifically for PCB manufacturing, there are 23 test methods and 35 related documents in TM650. In addition, there are 18 documents jointly issued by electronic industry associations and other industry associations. For those who need these documents, the information is already very rich, and almost all possible combinations of materials have been covered.

I definitely do not recommend that you check every document, but they are all related to PCB testing. If you start from IPC-6012, you can do almost all the tests in the PCB testing field, but not all tests are needed for your newly approved supplier, and some are even unnecessary. Some of the parameters that need to be tested include the plating thickness of the plated through hole (PTH) hole wall and pad, the curing of the solder mask, the resistance of the conductive anode glass fiber (CAF), and the cleanliness. Now, let's take a look at what we can get from these tests, and what reliability issues might have to do with the results of these tests.

I started with the first layer of the PCB manufacturing process. The production of high-quality printed circuit boards must first start here, and every step after that will increase the chance of causing circuit board failure. The CAF test is used in the blank circuit board manufacturing process to determine whether the conductive chemicals used in the manufacturing process will remain inside the PCB, and these residues will produce electrochemical migration. This is the same as the dendritic growth found on a PCBA filled with components. No matter where the electrochemical migration takes place, as long as there are conductive residues, moisture and potential differences, the risk of electrical leakage and dendritic growth of the circuit board during operation will increase.