2D simulation
（Analysis time is short and suitable for simple analysis）
3D simulation
（Analysis time is long and suitable for more detailed analysis）
Concentration of strain and stress
2. Analysis items of the stress simulation
Simulation items
Output
Study of high reliability PKG structure
(Variation of thickness of longitudinal structure etc.)
Optimum thickness and size
Optimization of physical property of material
Optimum physical property and material
Verification of PKG internal stress and PKG bow of unit PKG
Internal stress value and bow value
Lead deformation by the upper load after PKG assembly PKG
Stress concentration point and stress value
PKG deformation by three point bending
Stress concentration point, stress value and bow
Verification of lead deformation shape by upper load
Stress concentration point and lead deformation shape
Life time estimation of solder junction using the heat cycle
Soldering strain value and cycle number for life time estimation
Verification of land size for the purpose of reliability improvement
Optimum land size
Detachment of chip and resin
Internal stress value
Chip bending
Stress value
Assembling solder strain of chip resistance and its countermeasure Sim
Soldering strain value and countermeasure position
3. Simulation sample
■Conditions
Perform the thermal cycle of -40℃⇔125℃ for QFP type and BGA type
Chip stress and bow of PKG were measured when the temperature is decreased from 180℃ to 25℃（room temperature）
3-1. Analysis of QFP（Gull wing） type
Assemble QFP on printed circuit board
（1/4 model）
Enlarged view of Lead （Gull wing）
Simulation results
（Soldering strain by thermal stress）
Enlarged view of simulation results
（Top part of lead）
Enlarged view of simulation results
（Heel part）
↓
According to this strain distribution figure, it is realized that a large strain is generated at the heel part of the lead (yellow part of the right figure).
■Cross sectional view of real ruptured lead
The rupture point coincides well with the yellow part of the simulation results
Failure part of 144pin TQFP
Failure part of 176pin LQFP
3-2.
Analysis of BGA（Soldering ball） type
Assemble BGA on the printed circuit board
（1/4 model and full model）
Enlarged view of soldering ball
（PKG part is hidden）
Simulation results
（Soldering strain by thermal stress）
The strain concentrates not on the printed circuit board but inside PKG and in particular a large strain is generated at the corner ball.
Enlargement of simulation results
Upper surface of corner ball
Lower surface of corner ball
3-3. Analysis of PKG chip stress (internal stress) and PKG bow
1/4 Model of PKG
Chip stress results（Internal stress）
Bow of total PKG
With the results of above described simulation, the reliability of PKG is improved by modifying the material, structure and size to reduce strain and stress.
