During the PCB manufacturing and assembly process, the failure of tinning pads is a difficult problem that engineers often encounter. As a professional PCB manufacturer, we are well aware of the impact of this problem on product quality and production efficiency.

Five main reasons why the pads are not tinned

1. Surface oxidation (the most common problem)

Copper layer oxidation: copper oxide (CuO) or cuprous oxide (Cu₂O) is formed when exposed to air
Surface treatment layer failure:
HASL tin layer oxidation
ENIG nickel layer corrosion (black nickel phenomenon)
OSP organic protective film degradation

Silver layer sulfide

🔍 Identification features:

Oxidized pads appear dark black, brown or rainbow, and lose their metallic luster

2. Surface contamination

Fingerprint grease contamination

Flux residue

Silicon oil contamination (from peripheral sealing materials)

Dust particle adhesion

3. Improper welding process

Temperature is too low (lead-free solder requires 245-260℃)

Insufficient time (<2 seconds)

Insufficient flux activity

Oxidation of soldering iron tip

4. PCB manufacturing defects

Insufficient copper foil purity
Poor surface treatment process:
Insufficient immersion gold thickness
Porous immersion tin layer
Uneven OSP coating

Improper storage conditions (temperature and humidity exceed the standard)

5. Environmental factors

High humidity (RH>60%)
Sulfur/chlorine-containing industrial atmosphere

Condensation caused by drastic temperature changes

Professional solutions

1. Preventive measures
Measures Implementation method Effect
Nitrogen packaging Nitrogen-filled seal + desiccant Extend the shelf life to 12 months
Vacuum storage 20-25℃/30-50%RH environment Prevent oxidation and moisture intrusion
Surface treatment optimization ENIG to ENEPIG Solve the black nickel problem
2. On-site treatment method
For slight oxidation:
Wipe with special PCB cleaner (such as IPA)
Lightly brush the pad with a fiber pen (800 mesh or more)

Apply ROL1 grade active flux

For severe oxidation:

Plasma cleaning (best solution)
Microetching (5% citric acid solution)

Pre-tinning

3. Welding process adjustment

Welding parameter recommendations:
1. Lead-free solder (SAC305)
Soldering iron temperature: 350±15℃
Contact time: 3-4 seconds

Flux: ROL1

2. Leaded solder (Sn63Pb37)

Soldering iron temperature: 330±20℃
Contact time: 2-3 seconds

Flux: ROL0

Quality acceptance standards

According to IPC-A-610G Class 2 standard:
Pad wetting angle should be <90°
Tinning area should be ≥75%

Non-wetting or de-wetting is not allowed

Our quality commitment

As a professional PCB manufacturer, we provide:
12-month pad solderability guarantee (ENIG process)
Wet balance test report for each batch
Customized surface treatment solution

Professional storage and logistics solution

Contact PCBAMake technical team now to get the pad solderability optimization solution for your product.