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In-situ measuring module for transfer molding process monitoring
Keywords: Process Monitoring, Transfer Molding, Quality Assurance
While Moore's Law is slowing down heterogeneous integration and System-in-Package (SiP) are taking up the challenge towards further miniaturization. To ensure reliability of these packages often encapsulation by transfer molding is used providing a highly productive and cost effective device housing. Though transfer molding is the dominant process for microelectronics encapsulation, the process details are typically not accessible directly but only via machine settings. To understand more of the mold process further research needs to be conducted to get inside information from the process. The transfer molding process starts with the insertion of devices prone to encapsulation and a mold compound pellet in a hot transfer molding tool. After insertion the tool closes and vacuum is applied. A plunger transfers the molten encapsulant via channels and gates into the mold cavity. Time and temperature dependent EMC cure reaction mainly predetermines the flow behavior in the mold tool. After initial melting the Newtonian behavior of EMC rapidly becomes visco-elastic. With further reaction progress a solid 3D-network of crosslinked molecules is formed. Parameters like injection time and in mold cure time have to be adapted to fill the mold cavity and eject the product quickest possible. Today the process engineer typically works on a kind of a black box. Therefore a solution to in-situ measure process related data and EMC properties is valuable to allow a consistent process documentation according to DSC determinations or simulation data. Furthermore the data can be used to automatically control machine parameters, to economize the transfer mold process and to validate simulations. A sensor based system was developed to in-situ measure transient material data and process parameters. The temperature of the tool and melt front, the cavity pressure and cure related dielectric material data was measured with a first prototype. A substrate based sensor using an interdigital pattern was used to measure cure related properties of EMC. The substrate was used as a sensor shuttle to also measure the temperature of the melt front. In addition, commercially available discrete sensors where used to measure temperature of the tool near the gate and the cavity pressure. The results of in situ measurements indicate a difference between built in machine sensors and in situ measuring equipment. Applicability of in-situ dielectric measurement was proven and the data was correlated with reaction conversion based on DSC analysis. The in-situ data of dielectric properties like the capacity of the interdigital structure show a change of a factor 100 from uncured to cured status. Proven this the in-situ concept can be used to calculate the in-mold-cure-time based on material properties online and adapt the process accordingly. Summarized this paper presents the development of a sensor based system to in-situ measure characteristic material properties and process parameters in a transfer mold machine. The in-situ measurement tool allows a live documentation, optimization and knowledge extension of transfer mold processes parallel to FEM simulation and external measuring like DSC analysis. The sensor approach can lead to material driven self-adjusting transfer mold machines with an economized process.
Ruben Kahle, Process Engineer
Technical University Berlin
Berlin, Berlin

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