Knowledge: Do you know what are the common defects of PCBS?

The assembly of modern PCBA electronic products is a complex comparative analysis process for enterprises. In the production process, circuit printing service PCB defects are caused by factors of PCB substrate and PCB board processing development. Next, we will introduce some common PCB defects and student reasons.

In the process of PCB manufacturing development, common PCB defects are: white spots, micro-cracks, bubbles, delamination, wet weaving, dew cloth, halo, solder resistance defects.

1. White spots

At the interleaving point of the glass fibers on the sheet surface, PCB fabrication company the resin separates from the fibers, and a white spot or "cross line" appears under the substrate surface.

The reason:

(1) The plate is subjected to improper mechanical external forces, china PCB resulting in the separation of local resin and glass fiber into white spots.

(2) Local plates are corroded by fluorine-containing chemicals, forming regular white spots (square in severe cases).

(3) The sheet will be subjected to thermal stress caused by improper management, which will also cause white spots and white spots.

2. Micro cracks

The microcrack problem can be defined as continuous white spots or "cross analysis streaks" appearing on the laminated substrate through the interior.

Cause: The main cause of microcracks in laminated matrix is the effect of mechanical stress.

3. Foaming

Imagine local separation, caused by local expansion between substrate layers or between substrate and conductive foil or between substrate and protective coating.

The reason:

(1) Plate pollution (oxidation, oil, glue marks and other alkaline pollution)

(2) The management of post-curing reaction time is insufficient, which is mostly manifested as foaming on both sides of one corner and dripping oil, which is found after spraying tin.

(3) In addition to the tin is not clean, there is a thin layer of tin on the surface of the plate, to spray tin, the tin on the surface of the plate processing will be melted by Chinese ink after high temperature materials are studied, forming bubbles.

(4) Ink in the hole before water vapor drying. After spraying, a ring bubble is formed at the edge of the concealed water hole.

During the welding process of PCB board, there is water vapor in the board, and bubbles are easily generated during reflow welding.

4. Layering

Imagine the separation between a substrate layer, an insulating substrate, and any one of the conductive or multilayer layers.

The reason:

(1) The lamination parameters are not set according to the development requirements of the specifications.

(2) Cleaning work is not in place, there are debris on the board, and delamination after welding.

5. Wet-weave fabric

The braided fibers completely cover the resin and are not broken on the substrate, presenting a braided pattern on the surface.

6. Expose fabric

The surface of the substrate is not completely covered by the resin, or the fabric fibers are not broken.

7. Halo

Damage or delamination of the substrate surface or underside usually occurs in the white area around the hole or other machining site.

The reason:

(1) The machine or rubber board is uneven, and there is a gap between the board and the rubber board structure.

(2) Sheet warping deformation, there is a certain gap between the development of sheets

(3) Milling cutter wear

(4) Inspectors do not know that there is a missing detection phenomenon in the second set of drilling halo standards.

8. Solder resistance defects

Solder resistance film is a kind of high temperature resistant coating material. In the process of PCB welding, solder joint defects easily lead to solder joint deposition in non-welded areas.

The reason:

(1) The space or air gap around the gasket components is too large.

(2) After the development of solder resistance printing, the baking time and temperature control of the plate is not enough, resulting in the solder resistance is not fully cured. After being affected by the high temperature environment of the furnace, the solder resistance layer appears layered foaming.

These PCB defects are an important factor affecting the quality defect rate of enterprise electronic technology products. To understand the causes of these defects and their development, we can improve the process in the electronic assembly process and improve the yield of our products.