Basic knowledge of reliability and analysis method of common quality problems of PCB

Date：2022-03-08 14:55:00 Views：1110

PCB has become the most important and key part of electronic information products. The quality and reliability level of the whole equipment determine the quality and reliability of the whole equipment. Due to the reasons of cost and technology, there are a lot of failure problems in the production and application of PCB. For the same failure mode, the failure mechanism is complex and diverse. Correct analysis ideas, careful logical thinking and diversified analysis methods are needed to find the real failure cause.

Background information is the basis of failure analysis of reliability problems, which directly affects the trend of all subsequent failure analysis and has a decisive impact on the final mechanism judgment. Therefore, before failure analysis, the information behind the failure should be collected as much as possible, usually including but not limited to:

(1) Failure range: failure batch information and corresponding failure rate

① If there is a problem with a single batch in mass production or the failure rate is low, the possibility of abnormal process control is greater;

② If there are problems in the first batch / multiple batches, or the failure rate is high, the influence of material and design factors cannot be excluded;

(2) Failure pre-treatment: before failure, whether PCB or PCBA has gone through a series of pre-treatment processes. Common pre-treatment includes pre reflow baking, lead-free reflow soldering, lead-free wave soldering and manual soldering. If necessary, it is necessary to know in detail the information of materials (solder paste, steel mesh, solder wire, etc.), equipment (soldering iron power, etc.) and parameters (reflow curve, wave soldering parameters, hand soldering temperature, etc.) used in each pre-treatment process;

(3) Failure situation: the specific information of PCB or PCBA failure, some of which have failed during pre-treatment, such as welding and assembly, such as poor weldability, delamination, etc; Some fail during subsequent aging, testing and even use, such as CAF, ECM, plate burning, etc; It is necessary to understand the failure process and relevant parameters in detail;

Failure PCB / PCBA analysis

Generally speaking, the number of failed products is limited, even only one. Therefore, the analysis of failed products must follow the principle of layer by layer analysis from outside to inside and from non-destructive to destructive. It is forbidden to destroy the failure site prematurely:

(1) Appearance observation

Appearance observation is the first step of failure product analysis. Through the appearance of the failure site and combined with the background information, experienced failure analysis engineers can basically judge several possible causes of failure and carry out targeted follow-up analysis. However, it should be noted that there are many ways to observe the appearance, including visual observation, hand-held magnifying glass, desktop magnifying glass, stereo microscope and metallographic microscope. However, due to the difference of light source, imaging principle and observation depth of field, the morphology observed by the corresponding equipment needs to be comprehensively analyzed in combination with equipment factors. Do not judge rashly to form preconceived subjective conjecture, so that the failure analysis enters the wrong direction and wastes valuable failure products and analysis time.

(2) In depth nondestructive analysis

For some failures, only appearance observation can not collect enough failure information, and even failure points can not be found, such as delamination, false welding and internal opening. At this time, further information collection needs to be carried out with the help of other nondestructive analysis methods, including ultrasonic flaw detection, 3dx-ray, infrared thermal imaging, short-circuit positioning detection, etc.

In the stage of appearance observation and nondestructive analysis, it is necessary to pay attention to the common or different characteristics between different failed products, which can be used as a reference for subsequent failure judgment. After enough information is collected in the nondestructive analysis stage, targeted failure analysis can be started.

(3) Failure analysis

Failure analysis of failed products is indispensable and the most critical step, which often determines the success or failure of failure analysis. There are many methods of failure analysis, such as scanning electron microscope & element analysis, horizontal / vertical section, FTIR, etc., which will not be repeated in this section. At this stage, the failure analysis method is important, but what is more important is the insight and judgment of the defect problem, and a correct and clear understanding of the failure mode and failure mechanism, so as to find the real failure cause.

Bare board PCB analysis

When the failure rate is very high, it is necessary to analyze the bare PCB, which can be used as a supplement to the failure cause analysis. When the failure reason obtained in the failure product analysis stage is that a defect of the bare board PCB leads to further reliability failure, if the bare board PCB has the same defect, after the same treatment process as the failed product, it shall reflect the same failure mode as the failed product. If the same failure mode does not reappear, it can only show that the cause analysis of failed products is wrong, at least not comprehensive.

Recurrence test

When the failure rate is very low and can not get help from the bare board PCB analysis, it is necessary to reproduce the PCB defects and further reproduce the failure mode of the failed products, so that the failure analysis forms a closed loop.

Facing the increasing number of PCB reliability failures, failure analysis provides important first-hand information for design optimization, process improvement and material selection, and is the starting point of reliability growth.

The above is the content related to the analysis methods of common quality problems of PCB in core detection and small editing. I hope it will be helpful to you. Chuangxin testing is a professional testing organization for electronic components. At present, it mainly provides integrated circuit testing services such as capacitance, resistance, connector, MCU, CPLD, FPGA, DSP and so on. Specializing in functional testing of electronic components, incoming appearance testing of electronic components, anatomical testing of electronic components, acetone testing, X-ray scanning testing of electronic components and RoHS component analysis testing. Welcome to call, we will serve you wholeheartedly!