Author Contributions
Conceptualization, R.K. and T.G. (Thomas Guenther); methodology, R.K.; simulation, R.K.; experiments, P.W. and R.K.; characterization, R.K., M.H., and M.S.; writing—original draft preparation, R.K.; writing—review and editing, M.S., T.G. (Thomas Guenther), T.G. (Tobias Groezinger), and A.Z.; supervision, T.G. (Thomas Guenther) and T.G. (Tobias Groezinger); project administration, R.K.; funding acquisition, T.G. (Thomas Guenther) and A.Z.
Figure 1.
PCB with mounted devices (CR1206, CR0603, MLF28, DO1608C).
Figure 1.
PCB with mounted devices (CR1206, CR0603, MLF28, DO1608C).
Figure 2.
CAD model of the demonstrator for investigating the implementation of thermoset injection molding for thin-walled encapsulations of board-level packages.
Figure 2.
CAD model of the demonstrator for investigating the implementation of thermoset injection molding for thin-walled encapsulations of board-level packages.
Figure 3.
Molding tool insert for a 0.25 mm thick encapsulation.
Figure 3.
Molding tool insert for a 0.25 mm thick encapsulation.
Figure 4.
Fine mesh in the areas especially around the devices.
Figure 4.
Fine mesh in the areas especially around the devices.
Figure 5.
Exemplary fine mesh around the MLF with at least three elements over the wall thickness.
Figure 5.
Exemplary fine mesh around the MLF with at least three elements over the wall thickness.
Figure 6.
Simulated filling behavior (temperature scale) at different filling stages on the mounted (first row) and unmounted (second row) sides for an encapsulation thickness of 1 mm.
Figure 6.
Simulated filling behavior (temperature scale) at different filling stages on the mounted (first row) and unmounted (second row) sides for an encapsulation thickness of 1 mm.
Figure 7.
Comparative fill behavior from the simulation for (a) 1 mm, (b) 0.5 mm, and (c) 0.25 mm encapsulation thickness.
Figure 7.
Comparative fill behavior from the simulation for (a) 1 mm, (b) 0.5 mm, and (c) 0.25 mm encapsulation thickness.
Figure 8.
Setup for thermoset injection molding: (a) Arburg 375 V injection molding machine, (b) closed standard molding tool, and (c) attachment for processing of thermosetting plastics.
Figure 8.
Setup for thermoset injection molding: (a) Arburg 375 V injection molding machine, (b) closed standard molding tool, and (c) attachment for processing of thermosetting plastics.
Figure 9.
Test plan for the molding trials starting from top-left. A successful molding trial was to be followed by the green arrow and an unsuccessful molding trial was to be followed by the red arrow.
Figure 9.
Test plan for the molding trials starting from top-left. A successful molding trial was to be followed by the green arrow and an unsuccessful molding trial was to be followed by the red arrow.
Figure 10.
Filling behavior during MT01 on (a) mounting/front side but on an unmounted PCB, and (b) back side of the PCB.
Figure 10.
Filling behavior during MT01 on (a) mounting/front side but on an unmounted PCB, and (b) back side of the PCB.
Figure 11.
Encapsulated (1 mm thick) board-level package.
Figure 11.
Encapsulated (1 mm thick) board-level package.
Figure 12.
Significant uncovered areas of the package during mold trials MT02 due to the bent PCB.
Figure 12.
Significant uncovered areas of the package during mold trials MT02 due to the bent PCB.
Figure 13.
Pressure equalizing holes were also not useful in avoiding the PCB from bending during mold trials MT02.
Figure 13.
Pressure equalizing holes were also not useful in avoiding the PCB from bending during mold trials MT02.
Figure 14.
Original test plan superimposed by the actual path followed (blue dotted line).
Figure 14.
Original test plan superimposed by the actual path followed (blue dotted line).
Figure 15.
X-ray images of encapsulated devices (MT03): (a) resistors: voids in solder joint visible with no defect in the encapsulation; (b) MLF28: voids in solder joint, solder spatter and remnants of solder paste visible, and void in encapsulation in the gap under the device is possible; and (c) induction coil: voids in solder joint visible with no defect in encapsulation.
Figure 15.
X-ray images of encapsulated devices (MT03): (a) resistors: voids in solder joint visible with no defect in the encapsulation; (b) MLF28: voids in solder joint, solder spatter and remnants of solder paste visible, and void in encapsulation in the gap under the device is possible; and (c) induction coil: voids in solder joint visible with no defect in encapsulation.
Figure 16.
Images from the scanning acoustic microscopy at the interface of the PCB and the encapsulation. Except for a few delaminated areas (marked in red) at the edges, the encapsulation showed good adhesion with the PCB material.
Figure 16.
Images from the scanning acoustic microscopy at the interface of the PCB and the encapsulation. Except for a few delaminated areas (marked in red) at the edges, the encapsulation showed good adhesion with the PCB material.
Figure 17.
Results from microscopic analysis I. (a) Voids were noticed in the flow shadow region of the MLF. (b) An uncovered area (marked red) was noticed between two devices and the irregular shape of the glue around the induction coil caused irregularities. (c) Delamination of the encapsulation from the holder of the induction coil was noticed due to a lower thickness available in the lateral direction. (d) An offset is seen in the positioning of the induction coil and the resistor that enforced the presence of non-uniform encapsulation thicknesses on both sides of the device.
Figure 17.
Results from microscopic analysis I. (a) Voids were noticed in the flow shadow region of the MLF. (b) An uncovered area (marked red) was noticed between two devices and the irregular shape of the glue around the induction coil caused irregularities. (c) Delamination of the encapsulation from the holder of the induction coil was noticed due to a lower thickness available in the lateral direction. (d) An offset is seen in the positioning of the induction coil and the resistor that enforced the presence of non-uniform encapsulation thicknesses on both sides of the device.
Figure 18.
Results from microscopic analysis II. (a) Resistors and (b) MLF had a well-filled encapsulation when no irregularities in the device geometry or mounting were present. (c) The loose wires of the induction coil also had a well-packed encapsulation. (d) The thin gap under the MLF was also filled, though only partly.
Figure 18.
Results from microscopic analysis II. (a) Resistors and (b) MLF had a well-filled encapsulation when no irregularities in the device geometry or mounting were present. (c) The loose wires of the induction coil also had a well-packed encapsulation. (d) The thin gap under the MLF was also filled, though only partly.
Table 1.
Definition of different levels of packages according to Ref. [
1]. (IC: integrated circuit, RAM: random-access memory).
Table 1.
Definition of different levels of packages according to Ref. [
1]. (IC: integrated circuit, RAM: random-access memory).
Level | Stage |
---|
0 | IC chip |
1 | Encapsulated microelectronic package |
2 | Printed circuit board with various mounted devices |
3 | Multiple PCBs (e.g., RAM) integrated on a mother board |
4 | Housed electronics system (e.g., laptop computer) |
Table 2.
Key properties of material NU6110V according to Ref. [
15].
Table 2.
Key properties of material NU6110V according to Ref. [
15].
Material Property | Value |
---|
Density | 2.0 g/cm3 |
Glass transition temperature | 160 °C |
Thermal conductivity | 0.85 W/mK |
Coefficient of thermal expansion (20–105 °C) | 18 ppm/K |
Young’s modulus (flexural test) | 18 GPa |
Table 3.
Inputs used for the simulation.
Table 3.
Inputs used for the simulation.
Material | NU 6110 V |
---|
Melt injection temperature | 70 °C |
Mold tempering | 180 °C |
Flow control (flux) | 2 cm3/s |
Table 4.
Comparison of the CTE values of the two PCB variants (ppm/K).
Table 4.
Comparison of the CTE values of the two PCB variants (ppm/K).
Direction | Tg = 125 °C | Tg = 170 °C |
---|
X | 12.8 | 13.5 |
Y | 13.2 | 15.6 |
Z (below Tg) | 43 | 55 |
Z (above Tg) | 242 | 234 |