Causes and Countermeasures of expansion and contraction of PCB size

A substrate transfer from the inner line graphics processing by the number of pressing until the outer layer image transfer, will lead to different expansion board latitude.


From the PCB FLOW-CHART we can find out the cause and process of plate expansion and poor consistency of abnormal size:


The substrate material size stability, especially the size consistency between each of the laminated CYCLE supplier; even the same specifications of different substrate size stability of CYCLE were in the specifications, but due to poor consistency between the plates, can cause the trial to determine a reasonable inner compensation after, because of the difference of different batches of sheet the subsequent production of plate pattern size error; at the same time, there is an abnormal material is in the process of pattern transfer to outer shape during the process of plate found shrinkage; in the production process there have been individual batches of panel data in shape before processing in the process of measuring the plate width and shipment found the length of the element relative outer pattern transfer serious shrinkage rate, the ratio reached 3.6mil/10inch, the specific data see table; by tracing, the abnormal batches of plates in the outer laminate After the X-RAY measurement and the outer picture transfer rate are within the control range, at present, there is still no better method for monitoring in process monitoring;


Board design: conventional plate plate design for symmetrical design, the pattern transfer rate under normal circumstances the pattern size had no effect on the finished PCB effect; but part of a plate sheet in order to enhance the utilization rate, reduce the cost in the process of designing non symmetry structure and the use of graphics, size the consistency of different regional distribution of finished PCB will bring great influence, even during the processing of PCB we can in laser blind hole drilling and outer pattern transfer exposure / solder resist exposure / character printing process found in the asymmetric design of this kind of plate in the various aspects of the alignment degree relative to conventional plates are more difficult to control and improvement;


A layer image transfer process: here on the PCB panel size is refined to meet customer requirements plays a crucial role as a film; compensation rate transfer to provide bias which not only can directly cause the finished PCB pattern size can not meet the customer requirements, can also be caused by laser blind hole and subsequent the bottom connecting plate alignment caused by abnormal insulation performance and short circuit between LAYER TO until LAYER, and the outer layer image transfer process in general / blind alignment problem;


Based on the above analysis, we can take proper measures to monitor and improve the anomaly;

The incoming substrate dimensional stability and inter size consistency monitoring: substrate regularly for different suppliers to test for dimensional stability, from the same specification sheet tracking different batch latitude to the data differences, and the proper use of statistical techniques for material testing data analysis; and also can find the relative stable quality at the same time as the SQE supplier and purchasing department to provide more detailed data to choose suppliers; caused by plate occurred in the outer layer image transfer after expansion for serious substrate size stability of individual batches, currently only by measuring the shape of the production or shipment review measurement is made to it; but the latter group of higher management requirements that is easy to occur in a certain number of mass production of mixed plate;


Board design should be designed using a symmetrical structure, so that each board within the shipping unit to fight expansion remained relatively consistent; if possible, should communicate with customers in the process allows the advice of plate edge identification to etch / character etc. the shipping unit position in the board within the specific identification; the effect of this method in design of asymmetric mode plate will be more obvious, even if each plate internal asymmetric unit caused by individual size deviation, even so the bottom caused by abnormal connections can also be extremely local blind easily determine the abnormal unit and before shipment will pick the treatment, not causing the customer outflow package abnormal and complaints;


The production rate, the first to scientifically determine a transfer rate of plate production in order to reduce the production cost; change other suppliers substrate or P chip, this is particularly important; if it is found that plate out of control should be based on the unit tube hole is two times as drilling; for the conventional processing flow plate can according to the actual situation of clearance to adjust the outer pattern transfer film is two times magnification; such as drill plate, plate processing of abnormal need special care to ensure that the finished plate pattern size and the target to the pipe hole (two holes) of distance; the two layer plate plate collection rate list;


 

(Source: internal information)

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