Generally speaking, the number of failed products is limited, or even there is only one. Therefore, for the analysis of failed products, we must follow the principle of layer-by-layer analysis from outside to inside and from non-destructive to destructive. Avoid destroying the failure site prematurely:
(1) Appearance observation
Appearance observation is the first step in the analysis of failed products. Through the appearance of the failure site and combined with background information, experienced failure analysis engineers can basically judge several possible causes of failure and conduct targeted follow-up analysis. However, it should be noted that there are many ways of appearance observation, including visual inspection, handheld magnifying glass, bench magnifying glass, stereo microscope and metallographic microscope. However, due to the differences in light sources, imaging principles and observation depth of field, the morphology observed by the corresponding equipment needs to be comprehensively analyzed in combination with equipment factors. Avoid making hasty judgments and forming preconceived subjective speculations, so that the failure analysis goes in the wrong direction and wastes valuable failed products and analysis time.
(2) In-depth non-destructive analysis
Some failures can’t collect enough failure information by simply using appearance observation, and even the failure point can’t be found, such as delamination, false soldering and internal cracking. At this time, other non-destructive analysis methods need to be used for further information collection, including ultrasonic flaw detection, 3D X-RAY, infrared thermal imaging, short-circuit location detection, etc.
In the stage of appearance observation and non-destructive analysis, it is necessary to pay attention to the common or different characteristics among different failed products, which has certain reference significance for subsequent failure judgment. After collecting enough information in the non-destructive analysis stage, targeted destructive analysis can begin.
(3) Destructive analysis
Destructive analysis of failed products is essential and is the most critical step, often determining the success or failure of failure analysis. There are many methods of destructive analysis. Common ones such as scanning electron microscope & elemental analysis, horizontal/vertical sectioning, FTIR, etc. will not be repeated in this section. At this stage, although the failure analysis method is important, more important is the insight and judgment of defect problems, and a correct and clear understanding of failure modes and failure mechanisms is required to find the real cause of failure.
Bare board PCB analysis
When the failure rate is very high, the analysis of bare board PCB is necessary and can be used as a supplement to the failure cause analysis. When the failure cause obtained in the failure product analysis stage is that a certain defect of the bare board PCB leads to further reliability failure, then if the bare board PCB has the same defect, after going through the same processing flow as the failed product, it should show the same failure mode as the failed product. If the same failure mode is not reproduced, it can only mean that the cause analysis of the failed product is wrong, at least incomplete.
Reproduction test
When the failure rate is very low and no help can be obtained from the analysis of bare board PCB, it is necessary to reproduce the PCB defect and further reproduce the failure mode of the failed product to make the failure analysis form a closed loop.
Today, 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 for reliability growth. Since its establishment, the central laboratory of Xingsen Technology has been committed to research in the field of reliability failure analysis. Starting from this issue, we will gradually introduce our experiences and typical cases in reliability failure analysis.
Post time: Oct-18-2024
