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10 Common PCB Quality Problem You Should Know

1.Delamination

Delamination is a long-standing problem of PCB, the first ranking of the common problems. The causes may be as follows:

(1) Improper packing or preservation;

(2) The storage time is too long, more than the storage period, PCB board damped;

(3) Material or process problems;

(4) Material selection and poor distribution of copper surface.

The damp problem is more prone to happen, even if good packaging and the factory also has constant temperature and humidity warehouse, transportation and storage process are out of control. But it can be deal with the moisture, vacuum bag or conductive foil bag can be good protection and moisture intrusion, and the packaging bag requirements humidity indicator card. If the humidity card is found to exceed the standard before use, it can be solved by baking before on-line. The baking condition is usually 120 degrees, 4H.

Other possible causes include: Brown (black) poor, PP or inner board damp, PP glue quantity is insufficient, pressure abnormal, etc.. In order to reduce this problem, special attention should be paid to the management of PCB suppliers to the corresponding processes and delamination reliability tests. The reliability test of the thermal stress test as an example, King Sun through the standard test is more than 5 times and confirm the sample and mass production are no delamination, while the ordinary factory by the standard may be just 2 times to confirm once a few months. The analog mount IR test can also prevent more undesirable products from flowing out, which is a must for the excellent PCB factory.

Of course, the design of the company itself PCB design will also bring layered hidden dangers. For example, the choice of material Tg, most of all is not required, the PCB plant in order to save costs, certainly choose ordinary Tg materials, temperature resistance will be relatively poor. In the era of lead free to become mainstream, choose Tg 145 degrees or above is safe. In addition, the open large copper surface and too densely buried area are also the hidden dangers of PCB stratification, which need to be avoided in the design.

2.Solderability is bad

Solderability is also one of the most serious problems, especially the issue of batch size. The possible reason is the surface pollution, oxidation, black nickel, Nickel thickness exception, anti welding SCUM (shadow), storage time is too long, moisture absorption, anti welding PAD, too thick (repair).

Pollution and moisture absorption problems are relatively good to solve, other problems are more troublesome, and there is no way be found through IQC inspection.At this point, attention should be paid to the process capability and quality control plan of the PCB plant. For example, black nickel, need to look at the PCB factory is not gold, the gold drops the frequency analysis of whether their concentration is stable enough, whether the set of regular gold stripping test and P content test, internal solderability test whether to have good execution. If you can do it well, then there’s a very small chance of a lot of problems. The solder PAD and repair bad, you need to understand the PCB supplier for maintenance standards, inspectors and maintenance personnel have good job evaluation system, and define the pad dense area can not be repaired (such as BGA and QFP).

3.PCB bow and twist

The reasons may cause the PCB bow and twist, such as material selection, abnormal production process, bad control of heavy industry, improper transportation or storage, broken hole design is not firm, and the copper area difference of each layer is too large. The last 2 design problems need to be avoided in the early design review, and the PCB plant can be simulated to mount the IR condition to test, so as to avoid the poor bending of the furnace plate. For some thin plates, packaging can be required to press the wood pulp board before packaging, to avoid subsequent deformation, at the same time in the patch to add clamps to prevent the device too heavy bending board.

4.Scratch and copper exposure

Scratch and expose copper are the most difficult to test the management system and execution of PCB plant. The problem is serious and not serious, but it does bring quality concerns. Many PCB companies will say that this problem is hard to improve. The author has promoted a number of PCB factory scratches improve, found that many times is not bad, but to go to change, there is no power to change. DPPM has delivered a significant improvement in the PCB factory that is seriously promoting the project. So the solution to this problem lies in pushing and pressing.

5.Bad impedance

The impedance of PCB is an important index related to the RF performance of mobile phone board. The common problem is that the impedance difference between PCB batches is relatively large. Now a general impedance test is done in the PCB of the plate edge, not with the plate shipments, so let suppliers pay each shipment of the batch of impedance and test report for reference, but also requires the comparative data provide board size and board size inside edge.

6.BGA solder void

BGA solder holes may lead to poor performance of the main chip, and may not be detected in the test, hiding high risk. So now a lot of SMT factory will be affixed after the X-RAY inspection. The reason may be that the residual liquid or impurity in the PCB hole is vaporized at high temperature, or the laser hole pass on the BGA pad is not good. So now many HDI boards require plating filling or semi filling hole making, which can avoid the occurrence of this problem.

7.Solder Mask Peel-off

Such problems are usually PCB welding process control abnormal, or choose welding ink is not suitable (cheap, non – gold ink, not suitable for soldering flux), also may be SMT, heavy industry temperature is too high. In order to prevent the batch problem from occurring, it is necessary for the PCB supplier to formulate corresponding reliability testing requirements and control at different stages.

8.Vias Plugging bad

Vias plugging bad is mainly PCB factory technical ability is insufficient or simplify the process by, its performance for Jack is not full, hole ring has exposed copper or copper exposed false. It may lead to insufficient soldering capacity, short circuit with patch or assembly device, residual impurities in the hole and so on. The appearance inspection of this problem can be found, so it can be controlled in the feed inspection and require the PCB plant to improve.

9.Poor dimension

The size may be adverse for many reasons, prone to making PCB expansion process, suppliers adjust the drilling program / graphics / CNC ratio forming procedure, may cause mount prone to bias, with good structure problems. Because this problem is difficult to check out, can only rely on supplier good process control, so the supplier selection needs special attention.

10.Galvanic corrosion

The OSP process in the selective gold plate. Because the potential difference between gold and copper, copper pad in the process of OSP is connected with the large side will continue to lose electrons dissolved into 2 valent copper ions, resulting in the pad is smaller, subsequent component mounting and reliability.Although this problem does not occur frequently, it is designed to compensate in advance and set up special heavy industry conditions and limit the number of rework in the OSP process to avoid the problem.

The above problems have not been included in the short-circuit / open circuit, because this is the most basic problem of PCB, which board plant can not avoid, mainly to see whose process is relatively high.

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