During the process from the inner line pattern transfer of substrate to the outer line pattern transfer by pressing several times, the different longitudinal-weft expansion and contraction of the slab will be caused. From the entire PCB production FLOW-CHART, we can find out the reasons and processes that may cause abnormal expansion and shrinkage of board parts and poor dimensional consistency:
1. Dimensional stability of incoming substrate materials, especially the dimensional consistency between each laminating CYCLE of the supplier; Even if the dimensional stability of different cycles of the substrate of the same specification is within the specification requirements, due to the poor consistency between them, the graphic size of the subsequent mass production of the plate is out of line due to the difference between different batches of plate materials after the first plate trial production has determined a reasonable inner layer compensation. At the same time, there is a material anomaly that the board is found to shrink in the process of the outer pattern transfer to the shape process; In the production process, it was found that the width of the panel and the length of the shipping unit had a serious contraction in relation to the outer pattern transfer ratio during the pre-shape processing data measurement process, and the ratio reached 3.6mil/10inch. The specific data are shown in the following table. After tracing, it is found that the X-RAY measurement and the graph transfer ratio of the outer layer of the abnormal batch plate are both within the control range, and no good method has been found in the process monitoring at present.
2. panel design: the conventional panel design is symmetrical design, in the case of normal graphic transfer ratio has no obvious impact on the graphic size of the finished PCB; However, some board parts use the design of asymmetric structure in the process of improving the utilization rate of board materials and reducing costs, which will have a very obvious impact on the graphic size consistency of finished PCB in different distribution areas. Even in the PCB processing process, we can find that such asymmetric design plates in the laser blind hole drilling and outer graphic transfer exposure/solder resistance exposure/character printing process are more difficult to control and improve the alignment in each link than conventional plates.
3. an inner layer graphics transfer process: here the finished PCB board size meets customer requirements plays a very critical role; For example, if the film rate compensation of an inner LAYER graphic transfer has a large deviation, it can not only directly lead TO the finished PCB graphic size failing to meet customer requirements, but also cause the subsequent laser blind hole and its bottom connection disk to align abnormally, resulting in decreased insulation performance between LAYER TO LAYER until short circuit. As well as through/blind hole alignment problem in the process of outer pattern transfer;
Based on the above analysis, we can take appropriate measures to monitor and improve anomalies.
1. Monitoring of the dimensional stability of incoming materials and the dimensional consistency between batches of substrates: Conduct dimensional stability tests on substrates provided by different suppliers regularly, track the difference of the longitude and latitude data between different batches of sheet materials with the same specifications, and analyze the test data of substrates with appropriate statistical techniques; In this way, suppliers with relatively stable quality can be identified, and more detailed supplier selection data can be provided for SQE and purchasing departments. For individual batches, the poor dimensional stability of the substrate causes severe shrinkage of the sheet after the transfer of the outer pattern, which can only be detected by the measurement of the shape production first plate or the measurement during the shipment review; However, the latter has higher requirements for batch management, and it is easy to appear mixed plate in mass production of a certain number.
2. The design scheme of symmetrical structure should be adopted in the design of the assembly board, so that the growth and contraction of each shipping unit in the assembly board are relatively consistent; If possible, communicate with the customer to suggest that they allow the process side of the board to be etched/character and other identification of the location of each shipment unit in the assembly; The effect of this method will be more obvious in the plate designed in an asymmetric way, even if the size of each unit is out of whack due to the graphic asymmetry in each plate, and even the local blind hole bottom connection anomaly caused by it can be very convenient to determine the abnormal unit and pick it out before shipment, so as not to flow out and cause customer packaging abnormalities and cause complaints;
3. make the power of the first plate, through the first plate to scientifically determine the production of the first inner layer graphics transfer ratio; This is particularly important when changing substrates or P-chips from other suppliers to reduce production costs; When it is found that the plate is out of the control range, it should be processed according to whether the unit pipe position hole is secondary drilling; If the plate is a conventional processing process, it can be released to the outer graphic transfer according to the actual situation by adjusting the film ratio; If the plate is drilled twice, special care should be taken to handle the abnormal plate to ensure that the graphic size of the finished plate is the distance between the target and the pipe hole (secondary drilling). A list of first plate magnification of secondary laminates is attached;
4. Process monitoring: Use the inner layer target data of the outer or sub-outer layer plate measured during the production of drilling pipe position holes after its lamination to analyze whether it is within the control range and compare it with the corresponding data collected by the qualified first plate to judge whether the size of the plate has abnormal expansion and contraction. The attached table is for reference. According to the theoretical calculation, the ratio here should be controlled within +/-0.025% to meet the size requirements of conventional plate parts;
By analyzing the reasons for PCB size growth and contraction, find out the available monitoring and improvement methods, I hope that the majority of PCB practitioners can get inspiration from it, combined with their own actual situation, to find an improvement plan suitable for their own company.
English
Chinese