Reasons and countermeasures of PCB size shrinkage
From the substrate once the inner layer of the line pattern transfer by several times until the outer layer of the lamination line graphics processing, will cause the puzzle warp and weft to different expansion.
From the entire PCB production FLOW-CHART we can find out the reasons and processes that may cause the plate to contract anomalies and poor dimensional consistency:
1, the dimensional stability of the incoming material, especially the dimensional consistency of each laminate CYCLE suppliers.
Even if the same size base material CYCLE dimensional stability are in the specifications, but the consistency between the poor, can cause plate first plate trial to determine a reasonable first compensation after the inner layer due to different batches of sheet metal The difference between the subsequent mass production of graphics caused by over-size plate.
At the same time, there is another kind of material anomaly, which is the shrinkage of the sheet after the transfer of the outer pattern to the contouring process. In the production process, there are some batches of sheet pieces which are found in the process of measuring the shape before forming The length of the shipping unit relative to the outer graphics transfer ratio serious contraction, the ratio reached 3.6mil / 10inch.
2, the puzzle design: conventional board pieces are all symmetrical puzzle design, the transfer rate in the case of normal graphics on the finished PCB size does not have a significant effect; but part of the plate in order to improve the utilization of sheet metal, reduce Cost of the process and the use of asymmetric structure design, the distribution of different regions of the finished PCB PCB size uniformity will have a very significant impact, even in the PCB processing we can laser blind hole drilling Hole and the outer graphics transfer exposure / solder resist exposure / character printing process found that such asymmetric design of the board in all aspects of the alignment of the situation than the conventional plate is more difficult to control and improve;
3, an inner layer graphics transfer process: Here the finished PCB board size to meet the customer’s request plays a crucial role; such as a transfer of the inner layer of the film to provide a larger rate of compensation for its deviation can not only directly lead to finished PCB Graphic size can not meet customer requirements, but also lead to the subsequent laser blind hole and the bottom of the connection plate anomalies caused by LAYER TO LAYER insulation between the decline until the short circuit, and the transfer of the outer pattern of the pass / blind hole alignment problem.
Based on the above analysis, we can take appropriate measures to monitor and improve the anomaly:
1, the substrate material dimensional stability and inter-batch size consistency of monitoring: regularly to different substrates supplied by suppliers for dimensional stability testing, from tracking its different specifications with the same batch of latitude and longitude sheet data differences , And statistical techniques can be used to analyze the substrate test data to identify suppliers of relatively consistent quality while providing more detailed supplier selection data for SQE and purchasing departments. The poor dimensional stability caused by the plate after the transfer of the outer graphics serious shift occurred, the current only through the appearance of the production of the first board of the measurement or inspection to be measured at the time of shipment to find; but the latter on the batch management of higher requirements in the A number of mass production prone to mixed board;
2, the design of the puzzle should be symmetrical structure design, so that the various shipping units within the puzzle rose up to maintain a relatively consistent; if possible, should communicate with the client to allow it to allow the edge of the plate in order to etch / Characters and other identification of the shipping unit in the puzzle within the specific identification; this method in the asymmetric design of the effect of the plate will be more obvious, even if each puzzle due to asymmetric graphics caused by the various units of ultra-size Poor, and even the local blind hole connection caused by the exception may also be very convenient to determine abnormal cells and singled out before shipment processing, will not flow out of customer packaging caused abnormalities complaints;
3, making the first ratio of the first board, through the first board to scientifically determine the production of a sheet of the inner layer image transfer rate; in order to reduce production costs and change other supplier substrate or P film, this point is particularly important; when found to have Plate beyond the control range should be based on its unit bit hole is secondary drilling processing; such as conventional processing flow plate can be released according to the actual situation to the outer graphics transfer through the film magnification appropriate adjustments; Hole plate, the exception plate handling should be particularly cautious to ensure that the finished plate graphic size and the target hole to the hole (secondary drilling); with secondary laminated plate first plate magnification collection list;
4, process monitoring: the use of outer or sub-outer plate in its laminated X-RAY production hole hole when the measured plate inner target data to analyze whether it is within the control and Qualified first board to collect the corresponding data to compare the comparison to determine the size of the plate has abnormal rise and fall, there are tables under reference; after theoretical calculations, where the magnification should usually be controlled within +/- 0.025% to meet the conventional board The size of the piece requirements.