The reliable checking steps of SMT products .

Inspection purposes: to verify the reliability of solder joint strength for products manufactured by SMT.

Inspection method and process:

1.Solder joint appearance inspection

(1) Tools: X-Ray, 3-D microscope

(2) Main inspection, X-Ray mainly checks the shape of Solder Balls solder joint, BGA, LGA, QFN and other parts short circuit, displacement, Void size, etc.; 3-D microscope mainly checks the appearance of solder joints of lead leakage parts, tin angle Etc., as well as the outer surface of the BGA parts, the tin ball, the tin crack, the booty, etc.

(3) Inspection frequency:X-Ray: For BGA, every 1K of LGA products, check 1pannel has been imported3-D Microscope: For BGA, the first piece of LGA detects the appearance of five particles on the four sides and the center.           

Used for analysis of defective products

 (4) Inspection criteria:Void size acceptance criteria: IPC610D specification:

1), bubble volume ≤ tin ball volume 25% is acceptable bubble acceptance criteria:

2), bubble volume ≥ tin ball volume 25% is unacceptable           

Solder Balls displacement criteria:             

a: Tin ball offset PAD ≤ 25% is acceptable             

b: solder ball offset PAD ≥ 25% is unacceptable            Solder Balls short-circuit judgment standard: all short-circuited tin can not accept

2. Solder joint strength test

(1) Tools: push-pull machine and fixture

(2) Main inspection: resistance/capacitance/inductance/SOP, QFP and other original push-pull force measurementFrequency of inspection: new product / new original / new solder paste inspection; when bad analysis

(3) Inspection standards:At present, there is no inspection standard and experience value in the industry, except for the requirements of the customer.

3. Dye test

(1) Tools: stain, vacuum pump, oven, 3-D microscope

(2) Main inspection: Whether the tin balls of BGA parts are in good condition and whether there is tin cracking

(3) Inspection frequency: new product / new original / new solder paste inspection; when bad analysis

(4) Inspection criteria:          

It is not allowed to have a crack (color display) on a PCBA that has not done any reliability experiments.          

PCBA Crack after the Reliability test appeared at the solder joint end level ≤ 25% is acceptable.

 4. Slice inspection

(1) Tools: grinder, sealant, sandpaper, polishing powder

(2) Main inspection: Cross-section observation of the metallographic structure of the solder joint, and IMC forming, crystallization of the solder joint.

(3) Inspection frequency: new product / new original / new solder paste inspection; when bad analysis

(4) Inspection criteria:        

Sliced Solder Ball, QFP, SOP sample inspection:                  

a: Tin ball offset PAD ≤ 25% is acceptable

b: solder ball offset PAD ≥ 25% is unacceptable

c: Solder joint end short circuit and empty weld are rejected.

d: Crack is not allowed

5. Microstructure and elemental analysis

(1) Tools: SEM Electron Microscope & EDX

(2) Main inspection: microstructure of solder joints, IMC thickness measurement, and surface element structure analysis

(3) Inspection frequency: new product / new original / new solder paste inspection, when bad analysis

(4) Inspection criteria:Solder Joint IMC Thickness Test:          

PCB PAD end: 2-5um,

Component Substrate 1-3um

EDX judgment: usually Soder Ball and elemental composition: Sn/Ag/Cu 96.5%/3.0/0.5 where C, O atomic ratio is normal at 10%.It is normal that the content of the Elemental composition P of the IMC layer is about 9 to 11%.