HDI is the abbreviation of High Density Interconnector, which is a (technology) for producing printed circuit boards. It is a circuit board with a relatively high line distribution density using micro blind buried hole technology. HDI is a compact product designed for small-capacity users.
Regarding the quality issues and treatment of HDI-PCB manufacturing, Shenzhen Jingbang Electronics Editor has sorted out some issues for everyone, listed here and attached some treatment experiences, to share with you:
1. Poor solderability
Solderability is also one of the more serious problems, especially batch problems. The possible causes are board surface pollution, oxidation, black nickel, abnormal nickel thickness, solder mask SCUM (shadow), long storage time, moisture absorption, solder mask PAD, too thick (repair). Pollution and moisture absorption problems are relatively easy to solve, but other problems are more troublesome, and there is no way to find them through incoming material inspection. At this time, you need to pay attention to the process capabilities and quality control plans of the PCB factory. For example, for black nickel, you need to see whether the PCB factory outsources the gold processing, whether the frequency of analyzing its own gold wire solution is sufficient, whether the concentration is stable, whether regular gold stripping tests and phosphorus content tests are set up for detection, and whether the internal solderability test is well executed. If all can be done well, the possibility of batch problems is very small. For poor solder mask PAD and repair, you need to understand the standards set by the PCB supplier for maintenance, whether the inspectors and maintenance personnel have a good assessment and post system, and clearly define that dense pad areas cannot be repaired (such as BGA and QFP).
2. Delamination
Delamination is a long-standing problem of PCBs, and ranks first among common problems. The reasons for its occurrence may be as follows:
(1) Improper packaging or storage, dampness;
(2) Storage time is too long, exceeding the shelf life, and the PCB board is damp;
(3) Supplier material or process problems;
(4) Poor design material selection and copper surface distribution. The problem of dampness is relatively easy to occur. Even if good packaging is selected and there is a constant temperature and humidity warehouse in the factory, the transportation and temporary storage process cannot be controlled. The author once had the "fortune" to visit a bonded warehouse. Don't expect temperature and humidity management. The roof is still leaking and the boxes are directly in the water. However, dampness can still be dealt with. Vacuum conductive bags or aluminum foil bags can well prevent water vapor from intrusion. At the same time, a humidity indicator card is required in the packaging bag. If the humidity card is found to be over the standard before use, baking before going online can generally solve the problem. The baking conditions are usually 120 degrees and 4 hours. If there is a problem with the material or process at the supplier, the possibility of scrapping is relatively high. Common possible reasons include: poor browning (blackening), PP or inner layer board dampness, insufficient PP glue, abnormal lamination, etc. In order to reduce the occurrence of such problems, special attention should be paid to the management of the corresponding process by the PCB supplier and the reliability test of stratification. Taking the thermal stress test in the reliability test as an example, a good factory passes the standard requirement of no stratification for more than 5 times, which will be confirmed in each cycle of the sample stage and mass production, while an ordinary factory may only pass the standard twice, and confirm it once every few months. The IR test of simulated mounting can also prevent the outflow of defective products more, which is a must for excellent PCB factories. Of course, the PCB design of the design company itself will also bring hidden dangers of stratification. For example, the selection of the Tg of the board is often not required. In order to save costs, the PCB factory will definitely choose ordinary Tg materials, and the temperature resistance will be relatively poor. In the era when lead-free has become the mainstream, it is safer to choose Tg above 145°C. In addition, large empty copper surfaces and overly dense buried hole areas are also hidden dangers of PCB stratification, which need to be avoided during design.
3. Scratches and copper exposure
Scratches and copper exposure are the most challenging defects for the management system and execution of PCB factories. This problem is neither serious nor not serious, but it does bring quality concerns. Many PCB companies will say that this problem is difficult to improve. The author has promoted the improvement of scratches in many PCB factories and found that many times it is not that the improvement is not good, but whether to change it or not, and whether there is motivation to change it. All PCB factories that seriously promote the project have significantly improved the DPPM delivered. So the trick to solve this problem is: push and press.
4. Board bending and warping
The reasons that may cause PCB board bending and warping include: supplier material selection problems, abnormal production process, poor rework control, improper transportation or storage, insufficient design of broken holes, and large differences in copper area of each layer. The last two design problems need to be avoided through design review in the early stage. At the same time, the PCB factory can be required to simulate the mounting IR conditions for testing to avoid the defect of board bending after the furnace. For some thin boards, it can be required to pack the wood pulp board after pressing it up and down to avoid subsequent deformation. At the same time, a clamp can be added during patching to prevent the device from bending the board due to excessive weight.
5. Poor impedance
The impedance of the PCB is an important indicator related to the RF performance of the mobile phone board. The common problem is that the impedance difference between PCB batches is relatively large. Since the impedance test strip is generally made on the edge of the large PCB board and will not be shipped with the board, the supplier can be asked to provide the impedance strip and test report of the batch for reference each time it ships. At the same time, it is also required to provide comparative data of the board edge wire diameter and the board inner wire diameter.