Study on squeezing flow during nonisothermal embossing of polymer microstructures

Injection molding PMMA microfluidic chips can significantly improve the efficiency of chips forming. However, due to the coexistence of macro and micro effects in the injection molding process, the thickness uniformity of molding substrates is poor, which will seriously affect the thermal bonding quality of chips. In this paper, the effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding ratio and the quality of micro-channels was studied by experiments and simulations. The results show that when the following three conditions were satisfied during injection molding process, chips bonding ratio reaches to 93.9 % and the distortions of micro-channels caused by thermal bonding were acceptable. Firstly, the cover plates flatness error is smaller than 50-60 lm and substrates flatness error is smaller than 80-90 lm. Secondly, the maximum thickness difference of stack chips (cover plate stack with substrate) is smaller than 70-80 lm. Thirdly, chips thickness of the middle is larger than that of the two ends along their length direction and chips thickness distribute evenly along their width direction. These conclusions can be used for the parameters selection and moulds design during injection molding process of PMMA microfluidic chips.

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“…Thus chips were considered as the isotropic elastic body. The material properties of PMMA are shown in Table 3 ( Yao et al 2005).…”

Section: Materials Propertiesmentioning

confidence: 99%

The effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding ratio of chips

Chang

Song

et al. 2012

Microsyst Technol

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“…For other hot embossing applications, such as micro lenses and micro fluidics, the residual stress is undesirable as it affects the optical properties and the surface finish, both of which are not a major concern for piezocomposite moulds. Furthermore, it is known that wall climbing flow in non isothermal hot embossing can result in weld lines (Yao et al 2005) that act as points of weakness in the embossing. The single use nature of the moulds means that this weakness is not a major concern either, provided that the ceramic dough does not penetrate between the cracks.…”

Section: The Suitability Of Hot Embossingmentioning

confidence: 99%

1-3 Piezocomposites realised from small feature size, high aspect ratio, hot embossed moulds. Part I. Mould development

Clipsham

Button

2010

Microsyst Technol

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The industry standard process for the fabrication of 1-3 piezocomposites is limited to pillars with a width of greater than 100 lm. An alternative process, VP (viscous polymer) embossing, has the potential to overcome this limitation but is expensive because the mould is destroyed each time a piezocomposite it realised. Hot embossing offers the potential to cost effectively replicate piezocomposite moulds from a master so that the process can be moved out of the laboratory. In this publication, the fabrication of polymer moulds, consisting of an array of cavities, which have cavity walls of 30 lm and aspect ratios of 14 is presented. The quality of replication has been assessed, and the suitability of the process to produce moulds with smaller sized features and higher aspect ratios for high frequency piezocomposite applications is discussed. Piezocomposites for medical ultrasoundThe use of high frequency piezocomposites ([30 MHz) offers new opportunities for medical ultrasound in fields such as dermatology, ophthalmology and intravascular imaging (Lockwood et al. 1996). These opportunities are created because 1-3 piezocomposites provide an improved image quality over conventional, monolithic, transducers (Smith 1991). However, their use in high frequency medical ultrasound is limited because of their small feature size and high aspect ratio that becomes more demanding to manufacture with an increase in operating frequency.1-3 Piezocomposites consist of an array of piezoceramic pillars that are encapsulated in a polymer matrix (Tressler et al. 1999). They are typically made by a process called dice and fill (Safari et al. 1997). In this process, a pressed and sintered ceramic block has parallel slots cut into it. The block is then rotated by 90°and a further set of parallel slots are cut. This leaves an array of pillars that are upstanding from a stock, known as a bristle block. This bristle block is then backfilled with polymer, and the top and bottom faces are lapped to remove the stock and to ensure the faces are parallel.Unfortunately, dice and fill struggles to make pillars that are \100 lm wide (Safari et al. 1997) because in this size range, voids are also present in the ceramic material, which significantly reduces the survival rate of the pillars, and the yield of the devices. The spacing of the pillars, or kerf, is also limited by the width of the saw blade, and the range of designs are limited to straight sided pillars.Many researchers have developed processes that try to overcome the limitations of dice and fill, but few processes have made it out of the laboratory. One method that has shown promise is viscous polymer (VP) embossing (Abrar et al. 2004). In this process, a ceramic paste or dough, is pressed into a polymethyl methacrylate (PMMA) mould and is allowed to dry before the mould is dissolved. However, VP embossing is a lost mould technique which requires the mould to be destroyed each time the piezocomposite is realised, and is therefore expensive. One way to avoid this problem is to replicat...

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“…The difference in the maximum and minimum heights of the replicated pattern was 1.1 µm and the max height was shown at the central area of the replicated pattern. 11 As well as the central area of the replicated pattern, it is very important to observe the outer area in order to investigate the flow direction and characteristics of the polymer according to the pattern shape and forming condition during hot embossing. AFM was used to observe the profile of the crosssection of the replicated sample at the central area (1) of sample 1 of positions (1), (8), and (9).…”

Section: Polymethylmethacrylate(pmma)mentioning

confidence: 99%

Effect of forming conditions on linear patterning of polymer materials by hot embossing process

Lee

Kang

Youn

2010

Int. J. Precis. Eng. Manuf.

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In this work we demonstrate the hot-embossing process under different forming conditions such as forming temperature, load, and holding time in pressing, in order to determine the suitable conditions required for linear patterning on polymer plates (PMMA and PC). Results showed that the replicated pattern depth increased in proportion to an increase in the forming temperature, load, and time. The reduction of the workpiece thickness increased according to the holding time in the pressing process. In the process of time, the reduction ratio of the workpiece thickness decreased due to the surface area increment of the workpiece, while the pressure on the workpiece declined. In order to reduce the bulging ratio we introduced a temperature difference between the upper and the lower punch.

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Study on squeezing flow during nonisothermal embossing of polymer microstructures

Cited by 49 publications

References 16 publications

The effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding ratio of chips

The effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding ratio of chips

1-3 Piezocomposites realised from small feature size, high aspect ratio, hot embossed moulds. Part I. Mould development

Effect of forming conditions on linear patterning of polymer materials by hot embossing process

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