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PCBA electronic assembly EMS welding standard

Operation of electronic components

Operating guidelines:
a) Keep the workstation clean and tidy, and no food, beverages or tobacco products in the work area.
b) Minimize the operation of electronic components to prevent damage.
c) When using gloves, they need to be updated in time to prevent contamination caused by dirty gloves.
d) Do not touch the solderable surface with bare hands or fingers. Body oil and salt will reduce solderability, increase corrosiveness, and cause low adhesion after coating and lamination.
e) Do not use unapproved hand creams, they will cause problems with solderability and coating adhesion.

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f) The electronic components must not be stacked, otherwise it will cause mechanical damage. Special shelves must be used in the assembly area for temporary storage.
g) Parts without the ESDS mark should also be operated as ESDS parts.
h) The personnel must be trained and follow the ESD rules and regulations.
j) Unless there is suitable protective packaging, ESDS equipment must not be shipped.

Basic requirements for solder joints

1) Qualified solder joints must exhibit wetting characteristics, and the solder should adhere well to the surface of the metal being soldered. Wetted solder joints are characterized by a concave meniscus in the shape of the weld. The judgment is based on the contact angle of the interface between the solder and the pad, and the solder and the lead/weld end when wetted is small or close to zero. Generally, the range of solder alloys is very wide, which can show a contact angle from very low or even close to 0 degrees to a contact angle close to 90 degrees. If a part of the soldering surface is not wetted by the solder alloy, it is generally regarded as a non-wetting state, and the characteristic at this time is that the contact angle is greater than 90°.

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2) All tin-lead solder joints should have a bright, roughly smooth appearance, and form a concave meniscus on the surface of the welded metal.
3) Generally, the surface of lead-free solder joints is darker and rougher, and the contact angle is usually larger. The criteria for other aspects are the same.
4) The surface of solder joints formed by high temperature solder is usually darker.
5) The solder joints (rework) should be careful to avoid causing more problems, and the solder joints should also produce solder joints that meet the acceptance criteria.