In the whole PCB production flow-chart, we can find out the causes and processes that may cause abnormal board expansion and contraction and poor dimensional consistency:
1. Dimensional stability of substrate incoming materials, especially the dimensional consistency between each lamination cycle of the supplier; even though the dimensional stability of different cycles of the same specification of substrate is within the specification requirements, the poor consistency between them may cause subsequent batch production of panels due to the difference between different batches of panels after determining a reasonable inner layer compensation for the first panel trial production The shape and size are out of tolerance; at the same time, another material abnormality is that the board shrinks during the process of transferring the outer layer figure to the shape process; in the production process, there was a serious shrinkage of the transfer ratio of the outer layer figure between the panel width and the length of the shipping unit found in the data measurement process before the shape processing of individual batches of the board, with the ratio reaching 3.6mil/10inch. For the specific data, see The following table: after investigation, the X-ray measurement and the transfer ratio of the outer layer graphics of the abnormal batch of plates after the outer layer lamination are all within the control range, and at present, no better method has been found for monitoring in the process monitoring;
2. Panel design: the panel design of conventional panels is symmetrical, which has no obvious influence on the figure size of finished PCB when the figure transfer ratio is normal; however, some panels use asymmetric structure design in order to improve the utilization ratio of panel materials and reduce the cost, which will bring great significance to the figure size consistency of finished PCB in different distribution areas Obviously, even in the process of PCB processing, we can find that in the process of laser blind hole drilling and outer layer graphic transfer exposure / solder resist exposure / character printing, the alignment of this kind of unsymmetrical design board in each link is more difficult to control and improve than that of conventional board
3. Primary inner layer graphic transfer process: it plays a key role in whether the size of finished PCB meets the customer's requirements; for example, there is a large deviation in the film magnification compensation of primary inner layer graphic transfer, which can not only directly cause the finished PCB graphic size to meet the customer's requirements, but also cause the following laser blind hole and its bottom connecting disk to align abnormally, resulting in layer to The insulation performance between layers declines until the short circuit, and the through / blind hole alignment problem in the process of outer layer graphic transfer;
According to the above analysis, we can take appropriate ways to monitor and improve the abnormalities;
1. Monitoring of the dimensional stability of the incoming base material and the dimensional consistency between batches: regularly carry out dimensional stability test on the base material provided by different suppliers, track the longitudinal and latitudinal data differences between different batches of the same specification of the base material, and properly use statistical technology to analyze the test data of the base material; thus, the suppliers with relatively stable quality can also be found, as well as for SQE and procurement The purchasing department shall provide more detailed supplier selection data; for the serious expansion and contraction of the board after the transfer of the outer layer figure caused by the poor dimensional stability of the base material of individual batch, it can only be found by the measurement of the first board of appearance production or the measurement during the shipment review; however, the latter requires higher batch management, and mixed board is easy to appear in the mass production of a certain number;
2. For panel design, symmetrical structure design scheme shall be adopted to keep the expansion and contraction of each delivery unit in the panel relatively consistent; if possible, it is suggested to communicate with customers to allow them to mark the location of each delivery unit in the panel by etching / character identification on the process side of the panel; the effect of this method in the panel designed in asymmetric way will be more obvious Even if the size of each unit is out of tolerance due to the graphic asymmetry in each panel, or even the connection abnormality at the bottom of the local blind hole caused by it, it is very convenient to determine the abnormal unit and pick it out before shipment, so as not to cause complaints due to the abnormal encapsulation of customers due to outflow;
3. To make the first board, the first board is used to scientifically determine the transfer rate of the inner layer figure of the production board; this is particularly important when the base material or p-sheet of other suppliers is changed to reduce the production cost; when the board is found to be out of the control range, it shall be processed according to whether the unit pipe hole is a secondary drilling; if the board is a conventional processing flow, it can be released according to the actual situation The transfer to the outer layer shall be properly adjusted by the film magnification; in case of the secondary drilling plate, special care shall be taken to deal with the abnormal plate to ensure that the figure size of the finished plate and the distance from the target to the pipe position hole (secondary drilling); the collection list of the first plate magnification of the secondary laminated plate shall be attached;
4. Process monitoring: use the target data of the inner layer of the outer or sub outer plate in the X-ray production of the drilled pipe hole after lamination, analyze whether it is within the control range and compare it with the corresponding data collected by the qualified head plate to determine whether there is abnormal expansion and contraction of the plate size. The following table can be used for reference. After theoretical calculation, the multiplying ratio here should be controlled at + / - 0. Within. 025%, it can meet the size requirements of conventional plates;
Oct 31, 2019
