What are the possible problems in PCBA substrate production?
1. Various soldering problems
Blast holes in cold solder joints or tin solder joints
Before and after dipping soldering, the holes are frequently analyzed to find the places where the copper is stressed. In addition, the raw materials are inspected for incoming materials.
Blast holes or cold solder joints are seen after the soldering operation. In many cases, poor copper plating, followed by expansion during the soldering operation, creates cavities or blast holes in the walls of the metallized holes. If this is produced during the wet processing process, the absorbed volatiles are covered by the coating, and then driven out under the heating effect of the dip soldering, which will produce spouts or blast holes.
Try to eliminate copper stress. The expansion of the laminate in the z-axis or thickness direction is usually related to the material, which can promote the fracture of the metallized holes. Communicate with laminate manufacturers to obtain recommendations for materials with less z-axis expansion.
Second, the problem of bonding strength
Now it is a sign:
During the dip soldering process, the pad and the wire are separated.
When inspecting incoming materials, conduct adequate tests and carefully control all wet processing processes.
The detachment of the pad or wire during processing may be caused by electroplating solution, solvent etching, or copper stress during the electroplating operation. Punching, drilling, or perforation will partially detach the pad, which will become apparent during the hole metallization operation. In the process of wave soldering or manual soldering, the detachment of the pad or wire is usually caused by improper soldering technique or high temperature. Sometimes it is also because the original bonding of the laminate is not good or the thermal peel strength is not high, causing the pad or the wire to detach. Sometimes the design wiring of the printed board will cause the pads or wires to detach in the same place. During the soldering operation, the retained absorption heat of the component can cause the pad to detach.
Give the laminate manufacturer a complete list of solvents and solutions used, including the processing time and temperature for each step. Analyze whether copper stress and excessive thermal shock have occurred in the electroplating process.
Earnestly comply with recommended machining methods. Frequent analysis of metallized holes can control this problem.
Most of the pads or wires are detached due to lax requirements for all operators. If the temperature inspection of the solder bath fails or the residence time in the solder bath is prolonged, the detachment will also occur. In the manual soldering repair operation, the pad detachment is probably caused by the use of improper wattage electric ferrochrome and the failure to conduct professional process training. Now some laminate manufacturers have manufactured laminates with high peel strength levels at high temperatures for strict soldering applications.
If the detachment caused by the design wiring of the printed board occurs in the same place on each board; then the printed board must be redesigned. Usually, this does happen where thick copper foil or wires are at right angles. Sometimes this phenomenon occurs with long wires; this is because of the different coefficients of thermal expansion.
When PCBA is processed. Where possible, remove heavy components from the entire printed board or install them after the dip soldering operation. Usually use a low-wattage electric soldering iron for careful soldering. Compared with component dip soldering, the substrate material has a shorter duration of heating.
Third, the problem of excessive size change
Now it is a sign:
After processing or soldering, the size of the substrate is out of tolerance or cannot be aligned.
Fully carry out quality control during processing.
No attention was paid to the texture direction of the paper-based material, and the expansion in the forward direction is about half of the transverse direction. Moreover, the substrate cannot be restored to its original size after cooling. If the local stress in the laminate is not released, it will sometimes cause irregular dimensional changes during processing.
All the production staff are instructed to cut the board according to the same structural texture direction. If the size change exceeds the allowable range, consider switching to a substrate. Contact the laminate manufacturer for advice on how to relieve the stress of the material before processing.
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