Resin Smear

Defect Description

A thin layer of resin known as ‘resin smear’ or ‘epoxy smear’ that is formed between the copper interface and the PTH wall which creates a poor bond between plated copper and the hole wall including the inner plane copper interface [1].

Defect Formation Process(s)

Resin used in the PCB fabrication is a thermosetting polymer. If the drill bit is dull and speed/feed ratio is not optimized during drilling, the drill starts to extrude or punch through the PCB material. The resin becomes soft owing to excessive heat produced and is dragged across copper interfaces and the hole wall [2-3].

List of Tests to Precipitate this Defect

Failure Acceleration

Likihood to Precipitate Defect (condition)

Failure Mechanism(s)

Thermal Shock

• Thermal shock accelerates separation of copper-hole wall interface due to Coefficient of Thermal Expansion (CTE) mismatch

• Thermal shock accelerates fatigue of the thin layer of copper that is plated on irregular surface.

✔

Thermal Fatigue

Random Vibration (RS/ED)

• Random Vibration accelerates separation of the poorly bonded interface due to vibration-induced fatigue [4]

• Random Vibration accelerates fatigue cracking of the thin layer of copper that is plated on irregular surface.

✔/✇
(Defect orientation is sensitive to the vibration axes)

Mechanical Fatigue

Combined Environment

• Combination of thermal shock and random vibration

✔

Thermal Fatigue/ Mechanical Fatigue

Bend Test

• Bending can separate poorly bonded interface due to mechanical overstress

• Bending can cause fracture of the thin layer of copper that is plated on irregular surface.

✇

(Defect at a location with significant strain due to bending)

Mechanical Overstress



 [6]

References

[1] Viswanadham P., Singh P., Failure Modes and Mechanisms in Electronic Packages. New York: Chapman & Hall, 1998.

[2] Srinivasan M. N. et al., “Evaluation of drilled hole quality in printed circuit boards” Transaction of the ASME, vol. 117, no. 2, pp. 248-252, May 1995.

[3] Mayberry D. W., Bayley N. C., “ PC drilling: determining the speed-feed ratio” Electronic Packaing & Production, No. 1, pp. 99-110,1971.

[4] Pecht, M. Handbook of Electronic Package Design. New York: ASM International, 1991.

[5] IPC, PCB Quality Evaluation Handbook, IPC-QE-605A Revision A, 1999

Permission for pictures

[6] IPC, PCB Quality Evaluation Handbook, IPC-QE-605A Revision A, 1999


Top