PCB reliability problem and case analysis

PCB reliability problem and case analysis.

Since the early 1950 s, printed circuit board (PCB) has always been the basic construction of electronic packaging module, as the carrier of all kinds of electronic components and circuits of signal transmission hub, its quality and reliability determines the quality and reliability of electronic packaging.And with the electronic products miniaturization, lightweight and more functional requirements, as well as the process of lead-free and halogen-free, will be more and more high to the requirement of PCB reliability, so how to quickly locate PCB reliability problems and the corresponding reliability become one of the important topics of PCB enterprise.

solderability probelms;

cold solder joint

bonding problem

Layered plate blasting

open line in via hole copper

open line in laser hole

open line

open line ICD

short line CAF

short line ECM

bury board

In practical reliability problems failure analysis, the same failure mode, and its failure mechanism can be complicated, so like detective work, need the right analysis methods, rigorous logic thinking and diversified means of analysis, in order to find the real failure cause.In the process, any one of the links is slightly negligent, can cause "wrong case".

General analysis of reliability problems.

Background information collection

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

(1) failure scope: invalid batch information and corresponding inefficiencies.

If the problem of single batch in mass production, or if the efficiency is low, the possibility of process control abnormality is greater.

If the first batch has problems, or if the efficiency is high, the influence of material and design factors cannot be excluded;

Before the failure occurs, whether PCB or PCBA has passed a series of pre-treatment processes before the failure occurs.Common pretreatment include reflux before baking, / lead-free reflow soldering and/lead-free wave crest welding and manual welding, etc., when it is necessary to understand in detail all the materials used in the pretreatment process (such as solder paste, stencil, solder wire, etc.), equipment (soldering iron power, etc.) and parameters (flow curve and the parameters of the wave soldering, hand soldering temperature, etc.) information;

(3) failure situation: the specific information of PCB or PCBA failure, some of which have failed in the process of pre-treatment, such as welding process, such as poor weldability and layering;Some of them fail in subsequent aging, testing and even use, such as CAF, ECM, burning plate, etc.Detailed understanding of the failure process and related parameters;

Failure PCB/PCBA analysis.

In general failure product quantity is limited, even only one piece, so for the analysis of failure products must follow from outside to inside, from nondestructive to damage level analysis principle, the premature failure of avoid by all means failure site:

(1) appearance observation

Appearance observation is the first step in the failure product analysis, through the failure of the scene of the shape and combined with the background information, experienced the failure analysis of engineers to basic judge the failure of a number of possible reasons, and targeted for subsequent analysis.However, it is important to note that there are many ways to observe the appearance, including visual, hand-held magnifying glass, bench magnifying glass, stereoscopic microscope and metallographic microscope.However due to the different light source, the imaging principle and observe the depth of field, the corresponding equipment to observe the morphology need comprehensive analysis combined with the equipment factors, avoid by all means to determine formation preconceived conjecture, make failure analysis into the wrong direction, waste precious failure and analysis time.

(2) in-depth nondestructive analysis.

Some failure observed by appearance alone, can not be collected enough failure information, even can't find the failure point, such as layering, virtual welding, and inside, this time should be carried out with the help of other nondestructive analysis means further information collection, including ultrasonic testing, 3 d X - RAY and infrared thermal imaging, short circuit position detection, etc.

In the stage of appearance observation and nondestructive analysis, it is necessary to pay attention to the commonness or the characteristics of the opposite sex between different failures, which can be used for reference in the subsequent failure judgment.After collecting enough information in the nondestructive analysis phase, the targeted destruction analysis can be started.

(3) failure analysis

Failure analysis is indispensable and is the most critical step, which often determines the failure of failure analysis.There are many methods of destruction analysis, such as scanning electron microscopy & element analysis, horizontal/vertical slice, FTIR, etc., which are not described in this section.At this stage, the failure analysis method is important, but more importantly to the defects of insight and judgment, and the failure mode and failure mechanism has a clear understanding of the right, to find the real failure cause.

Bare board PCB analysis.

When the efficiency is high, the analysis of the bare board PCB is necessary and can be used as a supplement to the failure analysis.When failure product analysis phase is bare PCB board is the failure cause of a defect led to further the reliability of the failure, so if the bare PCB board with the same defect, after the same process as the failure product, should reflect the same failure mode and failure.If the same failure mode is not replicated, it can only be explained that the cause analysis of the defective product is wrong, or at least incomplete.

Repetition test

When the efficiency is low and cannot be helped from the PCB analysis of the bare board, it is necessary to carry out the reoccurrence of PCB defects and further the failure mode of the defective products, so that the failure analysis forms a closed loop.

In the face of increasing reliability failure of PCB, failure analysis provides important first-hand information for design optimization, process improvement and material selection, which is the starting point of reliability growth.Since its establishment, DTPCB has been devoted to the field of reliability failure analysis.