In the production, sometimes meet certain customer, request partial hole to plug hole, but can not completely plug full, the back of plug hole to prevent welding open window, and have depth request, popular call "PCB half plug hole".It is understood that such a client is to test in these holes, and will push the test probe into the hole.If there is too much ink in the hole, or the hole wall is polluted by ink, it can easily lead to false open road and affect test results.If the plug hole ink is too small, or not plug hole, can not satisfy the requirement of the plug hole.
Therefore, the depth of the plug hole must be controlled in the PCB production process and the hole is made according to the depth required by the customer.From the experience of conventional green plug hole, the depth of the control plug hole is not insufficient, but it is a relatively small hole depth and the accuracy of the specified plug depth.At present, there are two main kinds of methods: one is to fill the hole with full or a certain depth, and then the back of the plug is not exposed, and the part of the ink is flushed out through the development of the development to achieve the effect of the depth of the plug hole.The second is to strictly control the depth of the plug hole, then both sides of the hole are exposed.
The result of the test is that the plate surface is clean and the depth of the hole can be controlled well.As can be seen from the above table, the depth of copper can reach 1.65mm for the diameter of 0.25 mm.The 0.3 mm hole is about 1.49 mm;The 0.4mm hole is within 1.32 mm range.To make the hole less ink, you can make it faster.It can also adjust the air source pressure, the size of the aluminum aperture, the blade Angle, etc.
Conclusion: the first method is to develop the ink in some holes by developing the ink to achieve the depth control of the plug hole. The advantage is that the process is simple and easy to operate, and the disadvantage is that it often has ink surface when developing.The depth is affected by the development parameters, so it is difficult to achieve optimal value at the same time considering the depth of control and the other conditions of the development of the plane.And the uniformity is relatively poor.In the second method, the process is long and the PCB production is relatively complicated, and it is often necessary to make the first plate to confirm the depth before the batch is born, but there is no need to worry about the surface contamination after the development.Two methods are used to make the ink-shape drawing of the plug hole.It can be seen that the direct plug hole controls more of the copper in the same depth, which is beneficial to the customer's test.In production, the author believes that two production methods should be selected according to the appropriate production yield, and adjust them appropriately to save cost and improve production efficiency.