PCB Blog - The quality of the PCB board affects the assembly of the process

After the PCB board is produced, the components need to be assembled before further delivery. At present, the common assembly methods include wave soldering, reflow soldering and a combination of the two. The quality of the PCB board has a great impact on the assembly quality of the three processes.

1. The effect of PCB quality on reflow soldering process
1.1 The thickness of the pad plating is not enough, resulting in poor soldering. The thickness of the coating on the surface of the pad to be mounted components is not enough. If the thickness of tin is not enough, it will lead to insufficient tin when melting at high temperature, and the components and the pad cannot be well welded. Our experience is that the tin thickness on the pad surface should be >100μ''.
1.2 The surface of the pad is dirty, causing the tin layer not to wet. If the board surface is not cleaned properly, for example, the gold board has not passed the cleaning line, etc., impurities on the surface of the pad will remain. Poor welding.

1.3 The wet film is offset on the pad, causing poor soldering. The pads where the components need to be mounted on the wet film offset will also cause poor soldering.
1.4 The pad is incomplete, causing the components to not be soldered or soldered firmly.
1.5 The development of the BGA pad is not clean, and there is a wet film or impurities remaining, which causes the soldering to occur without tin during mounting.
1.6 The plug hole at the BGA protrudes, resulting in insufficient contact between the BGA component and the pad, which is easy to open.
1.7 The solder mask at the BGA is too large, resulting in exposed copper in the circuit connected to the pad, and a short circuit of the BGA patch.
1.8 The spacing between the positioning hole and the pattern does not meet the requirements, causing the printed solder paste to be offset and short-circuited.
1.9 The green bridge between the IC pads with dense IC pins is broken, resulting in a short circuit due to poor solder paste printing.
1.10 The via plug hole next to the IC protrudes, causing the IC to not be mounted.
1.11 The stamp hole between the cells is broken and solder paste cannot be printed.
1.12 The identification light spot corresponding to the wrong fork plate is drilled wrongly, and it is wrongly pasted when the parts are automatically attached, resulting in waste.
1.13 Secondary drilling of NPTH hole causes large deviation of positioning hole, resulting in deviation of printed solder paste.
1.14 Light spot (next to IC or BGA), it needs to be flat, matte, and without notch. Otherwise, the machine will not be able to recognize it smoothly, and it will not be able to automatically attach the parts.
1.15 The mobile phone board is not allowed to return to nickel-gold, otherwise the nickel thickness will be seriously uneven. affect the signal.

2. The influence of PCB board quality on wave soldering process
2.1 There is green oil in the component hole, resulting in poor tin on the hole.
For the PTH that needs to be inserted into the component, no ring-shaped green oil is allowed in the hole, otherwise the tin and lead cannot be smoothly soaked along the hole wall when passing through the tin furnace, resulting in insufficient tin in the hole, so the green oil in the hole of the PCB board component should not be More than 10% of the hole wall area. And the number of holes containing green oil in the whole board should not exceed 5%.
2.2 The thickness of the hole wall plating is not enough, resulting in poor tin on the hole. If the thickness of the coating on the hole wall of the component is not enough, such as copper thickness, tin thickness, gold thickness, and ENTEK thickness are too thin, it will lead to insufficient tin (a phenomenon called "belly button" by customers) or air bubbles. Therefore, in general, the copper thickness of the hole wall should be above 18 μm. The tin thickness should be above 100μ''.
2.3 The roughness of the hole wall is large, resulting in poor tinning or virtual welding. The roughness of the hole wall is large, the coating is correspondingly uneven, and the coating is thin in some areas, which affects the effect of tin. So the hole wall roughness should be <38μm.
2.4 Moisture in the hole, resulting in virtual welding or air bubbles. The PCB board is not dried before packaging, or is packaged without cooling after drying, and it is placed for too long after unpacking, which will cause moisture in the hole, resulting in virtual welding or air bubbles. For the baking board, our experience is: under the condition of 110-1200C, the tin board is baked for 4h, and the gold board and the ENTEK board are baked for 2h. And the service life of the vacuum packaging should not exceed 1 year.
The 2.5-hole pad is too small, resulting in poor soldering. Component holes and pads are broken and chipped. The size of the pad is too small, resulting in poor soldering, and the pad should be 4>mil.
2.6 Hole viscera, causing poor tinning. Insufficient cleaning of the PCB board, such as the gold board not being pickled, will cause dirt residue on the holes and pads, which will affect the tinning effect.
2.7 The aperture is too small, the components cannot be inserted and cannot be welded. Thick plating in the hole, accumulation of polytin and green oil, etc., cause the hole diameter to be too small, and the components cannot be inserted, so it cannot be welded.
2.8 If the positioning hole is offset, the components cannot be inserted and cannot be welded. The offset of the positioning hole exceeds the standard. When the component is automatically inserted, it cannot be positioned accurately, and the component cannot be inserted. Will also not be able to solder.
2.9 The rocker exceeds the standard, resulting in the surface of the component being soaked in tin during wave soldering. For warpage, it should be controlled within 1%; board warpage with SMI pads should be controlled within 0.7%.

3. The effect of PCB quality on the hybrid assembly process
The influence of the quality of the PCB board on the hybrid assembly process, there is a complicated situation in the hybrid assembly, that is, for a board, there are mounted components and plug-in components on the component surface, and there are mounted components on the welding surface. The mounting process is as follows: : Reflow soldering on the component surface - red glue on the soldering surface - red glue cured on a baking board - wave soldering on the component surface. The problems in this process have been described above, but there is a special requirement: if it is a tin-sprayed board, the welding surface cannot be polytin, because if polytin is used, the components on the welding surface will be glued to the red glue. It falls off when passing through the tin furnace. Therefore, the tin thickness of the soldering surface should be strictly controlled, and the PCB board should be as flat and consistent as possible while ensuring the tin thickness.