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MOLDFLOW is a plastic injection molding simulation software developed by Autodesk. Widely used in the plastic molding industry, it is a well-known software for mold flow analysis. Professionals in related fields are likely familiar with its applications. Besides its basic injection molding functionalities, MOLDFLOW offers various modules tailored for different scenarios and processes. This article will not discuss the commonly known plastic injection molding simulation. Instead, we will focus on the "Microchip Packaging Module," a very important component of the software. This overview aims to provide newcomers with a basic operational workflow, serving as a useful reference for those beginning their learning journey.
The "Microchip Packaging Module" is used to simulate the process of plastic encapsulation of microchips. It can simulate situations such as encapsulant filling, substrate deformation, and wire deformation. This helps the electronic packaging industry in design and process evaluation.
The analysis content of microchip packaging includes filling, packing, die pad shift, and wire sweep. Therefore, in addition to simulating the filling process, simulating the shift of the substrate and wire is a major focus. To achieve this, the model must be divided into three objects for import: the encapsulant, the die pad (substrate/lead frame), and the wire.
Import Objects
The encapsulant and die pad must each be a single object. For the die pad, the import requirements depend on the simulation detail needed. If the focus is solely on the substrate, then just the 3D substrate model needs to be imported. For a more comprehensive simulation, you can import a combined 3D model of the substrate and lead frame, or even include the heat sink if necessary. However, the more objects combined, the more complicated it becomes to specify different materials, as this requires setting mesh surfaces individually. In MOLDFLOW, the wire is defined as lines rather than 3D objects, and there can be multiple wires.
It is recommended to save the encapsulant and die pad as "STP" files for import, while the wire should be saved as line elements rather than 3D, and thus imported as "IGES" files. It is advisable to import each object separately into a new study, process the surface mesh, and then combine them into the same study afterward.
It is recommended to first assign properties to the objects. Change the properties of the die pad to "Insert" and assign the wire to "Wire." Specify the material for both the insert and the wire, and set the wire diameter. Note: If the wire is too thin and breaks during the simulation, the wire sweep analysis will not yield any results.
Generate Dual Domain Mesh
Create Dual Domain mesh for each object separately
Check Mesh
Mesh Statistics → Check Mesh. Ensure there are no mesh anomalies in the mesh information.
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Set Mesh Properties
Normally, if you have previously set the properties for the solid (metal object), the surface mesh will inherit these properties once the mesh is generated. If you haven't set the properties earlier, make sure to set the properties for the surface mesh at this stage.
Boundary Conditions
Since it is necessary to analyze the shifts in the die pad and wire, which are related to stress analysis, boundary conditions must be set. Constrain the "nodes" that need to be fixed. For example, the parts placed against the mold should be set as fixed constraints.
Create 3D Mesh
Select one object as the primary study file, then add the mesh file of the other 3D object to it. For example, add the mesh file of the die pad to the study file of the encapsulant. At this step, only combine the encapsulant and the die pad; the wire mesh file is not needed yet!
When selecting the gate, it must be set on the nodes of the encapsulant. Therefore, it is recommended to turn off the CAD layers. The gate can be set anywhere on the surface of the solid, but if it is not set on a node, the simulation will fail with an error indicating that the fluid path cannot be found.
Note: If you want to draw the wire manually, you can do so in this study before generating the 3D mesh. Once drawn, generate the 3D mesh, and the wire mesh will be created along with it.
After adding the wire mesh, you can prepare for the simulation. Next, confirm the following:
1.Check if all properties have been assigned correctly.
2.Verify that the gate is set on the correct node.
3.Confirm that the Microchip Packaging Module is selected.
4.Choose the analysis sequence: Filling → Packing → Die Pad Shift → Wire Sweep.
5.Complete the process settings
If all the above are OK, start the analysis!
Analyze Results
The successful analysis results should include four major items: flow, stress, wire sweep, and die pad shift, along with core shift.
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Common Issues
Here are some explanations for warnings or error messages that may appear when the analysis fails:
1.Analysis could not be completed within the maximum incremental load steps:
The analysis fails to converge, indicating that the analysis will essentially fail. It is recommended to stop and make corrections. This issue is usually due to incorrect boundary conditions not providing proper constraints.
2.No elements from the injection point to the part:
There is an error in the plastic flow path, generally because the gate is not placed on a "node." Be cautious when selecting the gate. It is recommended to turn off CAD elements to ensure the gate is placed on the node.
3.The mechanical properties of the selected material are not specified or invalid, and there are issues when reading the stress analysis results:
This is typically due to the lack of specified parameters in the material library. Please check and ensure the necessary properties are defined.
