PCB multilayer circuit board has bubbles, which can be solved by X-ray nondestructive testing

PCB multilayer board is made of tin lead alloy, which can effectively ensure the corrosion resistance of PCB multilayer board and provide protective layer and welding layer at the same time.

The wires on both sides of the etched circuit diagram are copper wires, which are easy to contact with air to produce an oxide layer, which is corroded by acid-base media. Moreover, the circuit pattern etching process will produce side corrosion, which is easy to cause wire bridging and short circuit.

In the graphic electroplating process, tin lead alloy layer is widely used in PCB multilayer boards. It is not only used as the graphic metal anti-corrosion layer, but also provides the protective layer and welding layer for lead tin plates. Because of the pattern electroplating etching process, both sides of the wire are still copper layers after the circuit pattern is etched, which is easy to contact with air to produce oxide layers or be corroded by acid-base media.

Due to the superposition of multilayer circuit boards, if the gas is not completely removed during the lamination process, when the heat capacity is high, the temperature will cause the gas to expand, resulting in bubbles. In view of this phenomenon, PCB manufacturers will still produce bubbles after many tests and sampling in different environments (different temperature control).

The specific causes of bubbles are mainly reflected in:

1. Board surface pollution (oxidation, oil stains, glue stains, other alkaline pollution)

2. The post curing time is insufficient, and most of them are blistering and oil dropping on both sides of one corner, which is found after tin spraying.

3. Tin stripping is not clean, and there is a thin layer of tin on the board. After tin spraying, the tin on the board will top up the ink after melting at high temperature. Form bubbles.

4. The water vapor in the hole is not dried before printing ink. After tin spraying, circular bubbles will be formed at the edge of the hole containing water

The influence of bubbles generated by PCB is mainly reflected in:

1. Unpredictable poor electrical property, or unpredictable poor contact to the circuit;

2. Electromagnetic interference control descent

3. Reduced service life