Contents 1. Introduction and Background 2 1.1 Injection Moulding 2 2. Type of Machine 4 2.1 Horizontal Injection Moulding Machine 5 2.2 Vertical Injection Moulding Machine 5 3. Type of Materials 6 4. Advanced technology/ Recent Research 7 4.1 Injection Moulding for Precision Pre-moulded MEMS Package 7 5. Conclusion 11 6. References 11

1. Introduction and Background 2.1 Injection Moulding
Injection moulding [1] is a manufacturing process that inserting material at higher pressure into a closed, cold mould, with inverse of the desired geometric of the parts, where it solidifies to form part, then followed by mould opened to release the part, and the cycle repeats. Injection moulding is capable to repeatedly form identical discrete parts at a shorter turnaround time as compare to machining.
Injection moulding not necessarily rely on one material, there’s variety of materials for example polymer and metals that can be used to produce parts. In this paper, the scope focuses plastic injection moulding by using polymer. Polymer [2] is adapted from Greek as ‘many part’, which describes molecule composed of many identical parts that synthesized together to from a large macromolecules. Generally plastic injection moulding uses thermoplastic and thermosetting polymers. The plastic parts that can be formed by injection moulding range from small electronic components such as lid of air-cavity package, to body panels of cars. Due to the capability of plastic injection moulding to generate big varieties of parts from as small as miligrams to kilograms, thus, a measure of size named shot size is selected which is determined by the weight of resin that can be injected per cycle. Shot size range between 20grams to 20kilograms.
Figure 1: Injection moulding machine (Source: Modified from Wikipedia [1])

Basic plastic injection moulding machine (Figure 1 [1]), consists of two sections, the injection section and the clamping section which hold the mould. The injection section consist of hopper to feed resin, heavy steel barrel, heaters to melts resins, reciprocating screw for compression of the resin to effect the injection, and nozzle. The mould at the clamping section is a tool consists of at least two halves which is that the impression of the part to be moulded is cut. One half is called the cavity at the stationary plate and the another half Is called core that’s attached to the movable plate of the moulding machine, usually is more complicated inclusive of ejector pins so that the moulded part can be freed from the mould. There’s two plate mould, three-plate mould and hot runner mould available in the industry depends on the applications. Figure 2 shows example of Mould and the tools configurations.
Figure 2: Mould and Tools (Source: Unisteel Precision (M) Sdn Bhd Archive [3])

The operation sequence of injection moulding with the combinations of the injection section and clamping section as follows 1. Mould closed and empty, molten resin is ready in the injection unit 2. Injection – valve opens and reciprocating screw, forces molten resin through nozzle into the mould 3. Hold on – pressure is maintained during initial stage of cooling to minimize contraction. Once freezing starts, the hold on pressure is released 4. Screw back – valve closes, reciprocating screw rotates, closed-off nozzle pressure develops and screw moves backwards to accumulate a fresh shot of molten resin in front 5. Part cooling – the moulding in the mould has continued to cool, and when complete, the press and the mould open and part is ejected. 6. Repeats – mould closes and cycle repeats.
In order to produce good plastic parts, with an efficient plastic injection moulding manufacturing process, it’s recommended to consider below criteria 1. The type of injection moulding machine 2. The selection of the resin material 3. The selection of mould design and materials 4. Appropriate operation of moulding cycle
Important manufacturing process parameters of plastic injection moulding to produce optimum parts as below
1. Pressure,
2. Time,
3. Distance and
4. Temperature.
Insert moulding is an injection moulding process whereby plastic is injected into a cavity and round an insert piece, example lead frame placed into the same cavity just prior to moulding The results of insert moulding is a single piece with the insert encapsulated by the plastic. The insert can be made of metal or another plastic, and this was initially developed to place threading inserts in molded parts and to encapsulate the wire-plug connection on electrical cords. Insert Moulding is also used quite extensively in the manufacture of medical devices, the typical application of insert moulding include insert-moulded need hubs, and bifurcations, as well as encapsulated electrical components and threaded fasteners. The accuracies of insert placement and cavity features can be below 5 micron [4]

2. Type of Machine
Injection moulding machine can be categorize in hydraulic, mechanical and electric. There’s a lot of injection moulding machines available for different applications in the industries, for examples, horizontal injection moulding machine, vertical injection moulding machine, Single/dual/multi-colour injection moulding machine, toggle injection moulding machine, hydraulic clamp injection machine and etc [5]. The injection moulding machine tonnage varies from 50ton to 4000ton, to produce shot size of 20grams to 20Kilograms. In this paper, only two types of injection moulding machine to be discussed in this paper, horizontal injection moulding machine and vertical injection moulding machine for insert molding for pre-moulded package of semiconductor industries. 3.2 Horizontal Injection Moulding Machine
Horizontal injection moulding machine is very common and widely use in the industry as compared to other models. The benefits of horizontal injection moulding machine, the manufacturing process can be converted to automated process with the advantages of gravity, the use of three plates mould that perform the self degating to detach the runner to the runner bin and the part drops to part bin. The use of robotic arm to remove runner is common as well.
Figure 3: Horizontal Injection Moulding Machine (Source from Haifly [5])

2.2 Vertical Injection Moulding Machine
Figure 4: Vertical injection moulding machine (Source from online [6] )
Vertical injection moulding machine consists the same configuration as compare to horizontal injection moulding machine, the difference is it’s in vertical format (Figure 4) [6] . Vertical injection moulding is good to use for insert moulding application. Refers to Figure 5, the insert piece to be loaded on the mold cavity, mold closes and molten resin flow, hold on, followed by mould opened resultant in insert piece being encapsulated by plastic.
Figure 5: Insert Moulding Process

3. Type of Materials
Injection moulding machine can be classified in three categories, thermosets, thermoplastics and elastomers. Thermoset is non-recyclable plastics. Thermoplastic is recyclable similar to metal and further breakdown to two types, crystalline which the produce is opaque and amorphous which the product is transparent.
The recyclable refers to the materials can be repeatedly softened by heating and solidified by cooling. The molecules in the thermoplastics are held together by relatively weak intermolecular forces, it’s relatively soft and ductile. However, additive such as glass fiber, carbon, minerals can be added to the thermoplastics to strengthen the plastic properties. There’s a variety of thermoplastic grade in the markets for different application in the industry. (Figure 6).
Liquid crystalline polymer (LCP) is a thermoplastic material which can replace ceramics, and metals by its outstanding strength at extreme high temperatures and resistance to chemicals, weathering, radiation and burning. LCP is dimensional stable and can achieve heat deflection temperature up to 300 degree Celsius when reinforced with glass fiber. The dimensional stability of LCP allows it to be moulded into precision thin wall components in semiconductor industry.

Figure 6: Thermoplastics Selection Guide (Source from Plastic International [7])

4. Advanced technology/ Recent Research 5.3 Injection Moulding for Precision Pre-moulded MEMS Package
Micro-Electro-Mechanical Systems (MEMS) is the integration of mechanical elements, sensors, actuators, and electronics on a common silicon substrate through micro-fabrication technology which perform transducer functions for taking measurements or initiating physical actions. The application of MEMS technology in commercial products has drastically increased in recent years, for example in mobile phone, plastic packages on average, weigh approximately half of a ceramic or metal package of the same type. The reduction in weight and package footprint helps designers reduce the overall weight of their electronic products. Besides the performance and reliability, to stay competitively in the era of high technology innovation aggregating all kinds of complex consumer applications and quick time to market trend, cost becomes more and more crucial for commercial MEMS applications. Hence, the use of thermoplastic materials with pre-plated lead frames via injection insert moulding offers the most viable solutions for volume take-up at low cost.
High speed digital data link or optical MEMS require cavity packages that was made by ceramics or metal previously can now made by LCP thermoplastics, LCP offer attractive properties for semiconductor application such as low gas permeation, high temperature resistance, thermal stability and low dielectric constant with (3.1 at 1 MHz and 2.8 at 10GHz) [8] [9]. LCP has 10 times lower moisture diffusion barrier than epoxy and absorbs only 0.03% moisture [10]. LCP also has excellent dimensional stability when molding and creates precision parts having flat surfaces right out of the mould without additional rework. LCP has a lower coefficient of thermal expansion value. LCP packages are can be categorize as near-hermetic [11] packages which capable of passing traditional gross and fine leak testing per MIL-STD-883E standard.
Plastic MEMS packages are developed after the injection moulding technology emerged to high precision parts and resin industry has introduced resin material with higher melting points (>300 degree Celsius) and heat deflection temperature to sustain the lead free high temperature reflow process [4].
Figure 7a: Moulding After Assembly Process [3]

As compare to conventional transfer moulding process which the packages are encapsulated after wafer sawing, die attach to the lead frame, and wire bonding (Figure 7a). Air cavity pre-molded package can be produced when a plated lead frames are inserted to the core mould and high temperature LCP is injected and moulded around lead frames to create cavity wall, the package is now called air cavity package, then proceed for wafer sawing, die attach and wire bond (Figure 7b). After the die and interconnects are added to the package, the air cavity can be sealed with a plastic lead made of LCP as well. The lid can be sealed with an epoxy or some other method such as heat or laser.
Figure 7b: Moulding before assembly process [3] LCP package is near hermetic as there’s non chemical nor intermetallic layer between the LCP and the lead frame, the adhesion purely on mechanical, hence, there’s possibility of contamination at the bottom bond pad during the gel encapsulation process, if the selected gel the molecular size is small as compare to the bonding line. The encapsulation epoxy will seep through the clearance between the plastic-metal mating area during gel solidification in the oven. As a result, post cleaning process is introduced to remove the excess epoxy of the molded package before sawing singulation process. According to Longford and Radloff [4], with the near hermetic LCP pre-moulded package, the hermeticity of the MEMs product is capable to achieve JEDEC level 2 packages, although level 1 is the goal for the industries. The level 1 goal will not be far with technologies discussed next.
According to Huang [11], the hermeticity of pre-moulded LCP package can be improved by incorporated Nano-sized mineral fillers with large aspect ratio, adding adhesion promoters, compatibilizers and anti-oxidants to into the conventional LCP resin. LCP is a semi-crystalline thermoplastic which contains amorphous and crystalline region, there will be intermolecular gaps between the amorphous and crystalline region which allows contaminant molecules and moisture will infuse through, refer Figure 8.
Figure 8a: LCP microstructure original versus with additive (Source from [11])

Figure 8b: Molecules Penetration throughout LCP material (Source from [11])

Figure 9: Flow diagram of hermetic LCP nanocomposites (Source from [11])

The improvement of LCP to hermetic package with additive can be prepared by pre-mixing the nano-fillers and additive with glass fiber reinforced LCP and the LCP mixture is then flow through the injection moulding process to produce hermetic LCP nanocomposites pre-moulded package.

5. Conclusion
Injection Moulding for pre-moulded MEMS package with advantages of lower manufacturing cost as compare to transfer moulding and ceramic packages is shared. Besides, the hermeticity of LCP packages can be improved by adding nano-size fillers to the LCP matrix resin 6. References 7. [1] | [Online]. Available: https://en.wikipedia.org/wiki/Injection_moulding. | [2] | D. M. A. ali, MMFU5023 Lecture 4- Polymer Injection Process, 2015. | [3] | Unisteel Precision (M) Sdn Bhd, Precision Mold For Plastics, Archive Folder, 2008. | [4] | B. R. Andy Longford, "The Use of Pre-Molded Leadframe Cavity Package Technologies in Photonic and RF Applicatiions," SEMI Technology Symposium: International electronics Manufacturing Technology (IEMT) Symposium, pp. 348-352, 2002. | [5] | [Online]. Available: http://www.haiflymachinery.com/html_news/Injection-molding-machine-types-120.html. | [6] | [Online]. Available: http://img.xpandrally.com/pic/z19747c9-0x0-1/rotary_table_vertical_injection_molding_machine.jpg. | [7] | Plastics International, "Thermoplastic Selection Guide," [Online]. Available: http://www.plasticsintl.com/thermoplastic_selection_guide.html. | [8] | A.-V. Pham, "Packaging with Liquid Crystal Polymer," IEEE Microwave Magazine, vol. 12, no. 5, pp. 83-91, Aug. 2011. | [9] | E. C. Culbertson, "A new laminate material for high performance PCBs: liquid crystal polymer copper clad films," Electronic Components and Technology Conference, pp. 520-523, May 1995. | [10] | Celanese Corporation, "Vectra E130i Datasheet," Celanese Corporation , [Online]. Available: http://catalog.ides.com/Datasheet.aspx?I=43838&FMT=PDF&E=18952. [Accessed October 2015]. | [11] | M. Huang, "Development of hermetic LCP for electronic device packages," Electronics Packaging Technology Conference (EPTC), 2012 IEEE 14th , pp. 415 - 419, 2012. |