Prescale® refers to a pressure indicating sensor film that can measure pressure between any two surfaces that touch, mate, or impact. Prescale® is synonymous with the following other terms: Fujifilm Prescale®, Fuji Paper, Fujifilm Prescale® Film, Fuji Pressure Film, Fuji Pressure Paper, Prescale Film, Prescale® Fuji Film, Pressure Indicating Film, and Pressure Measurement Film.
Prescale® is a unique, affordable, and easy to use tool that reveals the distribution and magnitude of pressure between any two contacting, mating, or impacting surfaces. It is a Mylar®-based film that contains a layer of tiny microcapsules. The application of force upon the film causes the microcapsules to rupture, producing an instantaneous and permanent high-resolution “topographical” image of pressure variation across the contact area. Like Litmus paper, the color intensity of the film is directly related to the amount of pressure applied to it, the greater the pressure, the more intense the color.
Fig 1: Prescale® Film before and after Topaq® Analysis
Figure 1 shows the pressure distribution across a clamping application on Prescale® film. At left is the Prescale® film after pressure has been applied and removed. The image at right is the pseudo-color result after Topaq® analysis.
Prescale® has been successfully used to measure pressure distributions during the transfer molding of electronic components. This has been reported in the following article: Schreier-Alt T et al, “Simulation and experimental analysis of large area substrate overmolding with epoxy molding compounds,” Microelectron Reliab (2010), doi:10.1016/j.microrel.2010.10.008.
Schreier asserts that commercially available tools for simulation of transfer molding are not able to predict the filling behavior of polymers within thin but wide-stretching gaps. In addition, numerical simulations are poor predictors of molding behavior. In order to examine polymer flow behavior during transfer molding, this group measured the pressure within the mold cavity using Prescale® as shown in Figure 2
Fig 2: Transfer molding process with central injection of the molding compound. Step A: Pellet and substrate are inserted into the mold tool and preheated. The substrate can be equipped with electronic components or a pressure sensitive film. Step B: The plunger presses on the pellet, the pellet melts. Step C: The melted polymer is pressed into the cavity. After filling the cavity the material is pre-cured for 2 min. Step D: The plunger is removed together with the cull. The Prescale® and the substrate are removed.
The results of an actual Prescale® analysis are shown in Figure 3.
Fig 3A: PCB with imprints of the mold tool and removed epoxy molding compound with pressure sensitive film. 3B: Pressure distribution of a film gate by simulation (left) and sensitive film. 3C: Pressure distribution of a central pin gate by Prescale® pressure film and short shot experiment.