Quality problems and handling experience of HDI PCB manufacturing
1, The author has sorted out ten problems totally, and listed here with some treatment experience, and share with you:
1)[bad solderability] solder ability is one of the more serious problems, especially the batchIt may occur due to board surface pollution, oxidation, abnormal thickness of black nickel and nickel, anti-welding SCUM (shadow), storage time is too long, moisture absorption, anti-welding PAD, too thick (repair).Pollution and moisture absorption problems are relatively easy to solve, other problems are more troublesome, and there is no way to find through the incoming inspection, at this time need to pay attention to the PCB plant process capacity and quality control plan.Such as black nickel, it needs to see whether the HDI PCB factory turns out the gold, whether the analysis frequency of the liquid medicine in the gold line is enough, whether the concentration is stable, whether the regular gold stripping test and phosphorus content test are set to inspect, and whether the internal solder ability test is well executed.If all can be done well, then the possibility of batch problem is very small.However, if PAD and repair are defective, it is necessary to know the HDI PCB supplier’s standards for maintenance, whether inspectors and maintenance personnel have trained by good on-job assessment system, and at the same time clearly define that repairing cannot be carried out in areas with dense pads (such as BGA and QFP).
2)[layering] layering is a long-standing problem of HDI PCB, ranking the first among common problems.The causes may be as follows :
2, Improper packaging or storage, damp
3,The storage time is too long, exceeding warranty, and the PCB board is affected by damp;
4, Material or craft problems of the supplier;
5, Poor design and material selection and poor copper surface distribution.
6, Dampness problem is relatively easy to happen, even if choosing good package, the factory also has a constant temperature and humidity warehouse, but the transport and temporary storage process is out of control.The author once “had the honor” to visit a bonded warehouse, temperature and humidity management is not expected, the roof is still leaking, the box is directly in the water.However, moisture can be dealt with, the vacuum conductive bag or aluminum foil bag can be a good protection against water vapor intrusion, at the same time the packaging bag require to put the humidity indicator card.If the humidity card is found to be out of standard before using, it can be generally solved by baking before going online. The baking condition is usually 120 degrees and 4H.If there are problems in material or craft at the supplier’s side, the possibility of scrapping is relatively high.Common possible causes include: poor Browning(blacking), damp ingress of PP or inner laminate, insufficient amount of PP glue, abnormal compression, etc.
7, In order to reduce this problem, special attention needs to be paid to PCB supplier management of corresponding processes and hierarchical reliability testing.Take the thermal stress test in the reliability test as an example, a good factory can’t be stratified for more than 5 times, and it will be confirmed in each cycle of the sample stage and mass production, while an ordinary factory may only pass the standard for 2 times and only confirm once every few months.The IR test of the simulated mounting can also prevent more defective products from flowing out, which is necessary requirement for an excellent PCB plant.Of course, the PCB design of the design company itself will also bring the hidden danger of layering.For example, there is no requirement for the selection of plate Tg in many cases. In order to save cost, PCB factory will definitely choose ordinary Tg material, and its temperature resistance will be poor.In an age of lead-free become mainstream, or choose Tg above 145 ° C is safe.In addition, large open copper surface and too dense buried hole area are also hidden dangers of PCB layering, which need to be avoided in the design.[scratches and copper exposure] scratches and copper exposure are the defects that most test the management system and execution ability of PCB factory.The problem is neither serious nor serious, but it does raise quality concerns.Many PCB companies will say the problem is hard to fix.The author once promoted the scratch improvement of many PCB factories, and found that most of the time it was not because of bad modification, but whether to change or not, and whether there was motivation to change.
8, Any PCB plant that seriously promotes the project has a significant improvement in the DPPM delivery.So the trick is: push, press.4. [board bending and board warping] the possible causes of HDI PCB board bending and board warping include: material selection problem of suppliers, abnormal production process, poor control of heavy industry, improper transportation or storage, unstable design of broken holes, large difference in copper area of each layer, etc.The last two points of design problems should be avoided in the preliminary design review, and the PCB factory can be required to simulate the IR condition of mounting for testing, so as to avoid the bad bending of the plate after passing through the furnace.
9, For some thin plates, it can be required to pack after adding pressure up and down to wood pulp board, to avoid subsequent deformation, at the same time add clamping device to prevent overweight bending plate.5. [poor impedance] the impedance of HDI PCB is an important indicator related to the rf performance of mobile phone board, and the common problem is that the impedance difference between PCB batches is relatively large.Since the impedance test strip is generally made on the side of the big PCB board and will not be shipped with the board, we can ask the supplier to send the impedance strip and test report of this batch for reference every time the shipment is made. Meanwhile, the comparison data of the edge diameter of the board and the inside diameter of the board are needed .
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