In a research project being carried out by the IKV and KTP, the influence of geometric and process parameters on the quality of the screw connection in the direct assembly of thermosetting plastics has been analyzed. The research results show that, in addition to the geometric design, the production parameters offer additional optimization potential for the reliability of the screw connection. The compactness and curing degree of the parts exert the largest influence.

Encapsulation protects the sensitive sensor technology from external influences. The direct screw connection enables secure mounting of the module.

16:9

Higher Process Quality through Adjustment of the Production Parameters

Spritzgießen

Kunststoffverarbeitung: Verfahren

Verbindungstechnik

Schraubtechnik

Verbindungstechnik Verfahren

Duroplast-Spritzgießen

Duroplaste

Kunststoff Werkstoffe

Achieving a More Secure Connection with the Correct Design

The traditional markets for glass fiber-reinforced thermoplastics remain stable. Thermoplastic composites are gaining fast with 3D-printing and hybrid processing techniques. The fiber composite industry is tackling the recycling issue with pragmatic ideas.

The Oechsler Drivematic drive actuator can be integrated into the 3D-printed CFRP monocoque frame of an Arevo „e-bike“

The Manifold New Collection of Reactive Systems and Thermoplastic Composites

Glasfasern / -matten

Verstärkungsstoffe

Reaktionsharze

Kohlenstofffasern / -matten

Sekundärfasern

Kunststoff-Rezyklat

Fasern

Halbzeuge und Zwischenprodukte

Kunststoff-Halbzeuge

Verbundwerkstoffe / Werkstoffverbunde

Aramidfasern

Harzsysteme für Composite-Herstellung

Phenolharze

Harzwerkstoffe

Andere Werkstoffe

Werkstoffe für additive Verfahren

Harze, Epoxid

Duroplastische Werkstoffe

Faserverbundwerkstoffe

Hochleistungskunststoffe

Thermoplaste

Fiber-Reinforced Plastics

To meet stringent flame retardancy demands of areas such as transportation and electronics, components based on thermosets increasingly require a soluble, non-powder flame retardant (FR) due to low layer thicknesses in the final product or due to liquid processing methods. Two flame-retardants developed by Clariant meet these requirements.

20:7

Completely Halogen-Free Flame Retardancy of Epoxy-Fiber Composite Components

Füllstoffe für Kunststoffe

Flammschutzmittel

Additive

Avoiding Filter Effects of  Flame Retardants

Avient Corporation, Cleveland, OH/USA, presents Gravi-Tech density-modified thermoplastics that enable advanced metal plating surface treatments to deliver both the look and feel of metal in premium packaging applications.

“These metallization-ready grades give premium packaging manufacturers a simpler way to incorporate the luxurious look and weight of metal into their products,” said Matt Mitchell, director, global marketing of Specialty Engineered Materials at Avient

Metallization Grades for Luxury Packaging

Due to its high-performing properties polyetheretherketone thermoplastic polymer is being used more and more frequently in many products.

PEEK can replace fluoropolymers in cryogenic applications. Advanced Engineering Valves uses PEEK from Victrex for sealings in ball valves

Polyetheretherketone (PEEK)

Elektronik-Fertigung

Elektronik

Polyetherketon

Mikroelektronik

Kunststoff

Bauwesen

Baustoffe

Medizintechnik

Medizinprodukte

Delivering Efficiency Even in  Harsh Environments

For lightweight applications e. g. in automotive engineering BASF developed carbon fiber-reinforced polyphthalamide (PPA) grades with fillings of 20, 30 und 40 %.

The carbon fiber-reinforced PPA e. g. can replace aluminum and magnesium 

PPA Now with Carbon Fiber-Reinforcement

Automotive

Lightweight Metal Replacement

Teknor Apex presents three halogen-free FR glass-reinforced polyamide compounds with UL94 ratings of V0.

Application example: engine cover in the automotive industry

Polyamide

Technische Kunststoffe

Glass-Reinforced and Halogen-Free Flame-Retardant

The new mobile communications standard 5G is advancing steadily. This development is also increasing the demand for materials that facilitate and ensure the high transmission rates for 5G signals. Plastics manufacturer Covestro has presented a corresponding thermoplastic polyurethane (TPU).

Covers for cell phones must not only protect the devices from shocks, but also allow mobile signals to pass through without interference

Polyurethan

Cell Phone Covers Made from TPU

The transfer of foam injection molding from thermoplastic to thermoset processing has not yet been implemented in industrial practice. IKV Aachen has investigated this transfer and has precisely analyzed the economic efficiency of the process and the potential for lightweight construction.

Foamed thermosets can be used to produce low-density thermally resistant components at low cost

The Qualification of Suitable Foam Injection Molding Processes Enables the Use of Thermosets in Lightweight Construction Applications

Schaumspritzgießen

Excellent Resistance at Reduced Weight

Susanne Schröder will become editor-in-chief of the magazines Kunststoffe and Kunststoffe international on December 1, 2020. The current editor-in-chief Dr. Karlhorst Klotz will leave the company by mutual agreement.

Susanne Schröder will become editor-in-chief of the magazines Kunststoffe and Kunststoffe international on December 1, 2020. Until now she has been editor-in-chief of the trade journal FORM+Werkzeug

Werkzeuge für Leichtbauwerkstoffe

Präzisionswerkzeuge

Tiefziehwerkzeug

Dienstleistungen

Werkzeug-, Formen- und Modellbau

Werkzeugüberwachung

Toolmanagement

Werkzeugwechselsysteme, Spritzgieß

Kunststoffverarbeitung: Maschinen und Komponenten

Werkzeuge für die Kunststoffverarbeitung

Spritzgießwerkzeuge

Werkzeug- und Formenbau

Modulare Werkzeugsysteme

Absaugungen für Werkzeugmaschinen

Betriebsausrüstung / Betriebsmittel

Absaugvorrichtungen

Fluorkunststoffe

Werkzeugverwaltungssoftware

Prüfen von Kunststoffen

Messtechnik

Biokunststoffe

Presswerkzeuge, Kunststoff

Werkzeugreinigung, Kunststoffe

Standardkunststoffe

Kunststoffverarbeitung

Lohnfertigung

Kunststoffhandel

Handel

Betriebstechnik für Kunststoffverarbeitung (Peripherie)

Kunststofffasern

Kunststoff-Recycling

Kunststoff-Aufbereitung

Qualitätssicherung Kunststoff

Qualitätssicherung

Change in the Chief Editorial Office of Kunststoffe

The non fossil fuel-based portfolio offers same high quality and performance for applications in all industries.

The Bornewables portfolio is suitable for the production of the most demanding applications, including hygiene and food-contact

Gehäuse aus Kunststoff

Elektromechanik

Kühlkörper

Polyethylen

Polystyrol

Polypropylen

Kunststoff-Regenerate

Borealis Launches Portfolio of Circular Polyolefins

The Danish company Plastix recycles old fishing nets and ropes. The granules produced are used by JSP International, among others, to manufacture expanded polypropylene (EPP).

11 % of the plastic waste in the sea comes from the maritime industry. For the recycling of old fishing nets and ropes, accurate sorting is very important

Expanded Polypropylene from Maritime Plastic Waste

Schaumstoffe und Vorprodukte

Schaumstoffe

Recycling

Umweltmanagement

Polypropylen-Compound

From Fishing Net to Particle Foam

The central issue in all polyurethane applications is the conversion from the past linear economy into a circular economy, and the use of sustainable raw materials in manufacturing. To do so, manufacturers are taking measures such as using bio-based raw materials, chemical recycling, and CO2 as a synthesis component. Digitalization, electromobility, autonomous driving and the construction industry are also driving PU development.

Insulation boards and metal composite elements are the primary applications for PU in the construction industry. Since buildings are  responsible for 40 % of global energy consumption, more efficient materials in this area can generate big savings, such as through improved insulations

Polyurethane (PU)

Bauchemie

Polyurethan-Schaumstoffe (PUR)

Baubetrieb / Bauwirtschaft

Windkraft

Energieerzeugung

Erneuerbare Energie

Sustainable Growth

Styrenics can be polymerized using different technologies and it can be modified with a range of copolymers. The resulting plastics offer a wide range of properties allowing to customize them for different applications. Because of this range of properties they are suitable for many industries. Strong demand is for example driven by the automotive industry, healthcare and the packaging industry.

Styrene copolymers are frequently used in the exterior of vehicles. The Chinese manufacturer Lixiang, for example, uses an ASA for the radiator grill of its electric vehicles

Styrenic Polymers

Verpackungsmaterial

Logistik

Styrol-Copolymerisate

Diverse Shapes and Applications

Lightweight construction, functionality and design are characteristic of material development in all areas of application for PC compounds, composites and films. The range of materials has enormous opportunities when it comes to the mobility of the future, lightweight structural construction with continuous fiber-reinforced composites, 5G technology and medical technology.

In electric vehicles, the original function of the radiator grille, namely to supply air to the engine, is no longer needed. It can therefore be used entirely as a design element, for example by integrating luminous logos and fade-out effects

Polycarbonate (PC)

Polycarbonat

Present in a Multitude of Trends

Thermoset Injection Molding of Packages for Electronic Devices

Thermosets are being increasingly used for packaging electronic devices, and offer good properties for this application. Direct overmolding of the components is particularly interesting here. However, achieving a successful product requires striking a balance between processability, thermal conductivity and reproducibility.

Thermoset materials have a track record of industrial use dating back to 1908 [1]. That makes them the oldest synthetic polymers. Even now, these materials are continually finding new applications. Thermosets reached a peak in the second half of the 20th century, when their good thermal and chemical resistance played a major role in most areas of application. However, they have diminished in importance in recent decades. Nevertheless, developments in the electronics and automotive industries have given thermoset components a new lease of life in recent years. A focus here is the protection of sensitive electronic devices, such as sensors. At Robert Bosch GmbH, too, ever more electronic devices are being provided with thermoset packages, often by means of direct packaging.

In direct packaging, an electronic device, for example a control unit or sensor, is directly overmolded with a thermoset molding compound. The thermoset forms at least an adhesive bond with the packaged components and, at the same time, often also forms the subsequent device package. The thermomechanical properties of thermosets are a special advantage here, especially the low thermal expansion and virtually isotropic properties in the plane. Seen quantitatively, thermoset molding compounds typically have a thermal expansion of the order of copper (17  ·  10–6  K-1 or aluminum (23  ·  10–6  K-1). The thermal expansion of the circuit board is similar to that of the molding compounds used. The nearer the coefficient of expansions are to one another, the lower the mechanical stresses are under cyclic thermal loads. Thermoset molding compounds therefore offer ideal prerequisites for use as encapsulating materials. A typical temperature application range for direct packaging is between –40 and 150 °C.

More Gentle Processing Compared  to Thermoplastics

The processing properties of thermosets also favor their use for packaging sensitive devices. During filling, i. e. when the degree of curing is low, thermosets show the lowest viscosity (mold temperature > material temperature). The encapsulation can therefore be done especially gently. With thermoplastics, the viscosity in the mold (mold temperature &lt; material temperature) increases rapidly and consequently the components to be encapsulated are subject to greater stress. In addition, very low-viscosity thermoset formulations exist for both transfer molding and injection molding, which allow very low cavity pressures to be realized [2]. A disadvantage of the materials is the curing that occurs during processing, the influence of which should always be taken into account in considerations about process reliability.

The advantages of direct packaging that should be particularly stressed are, among others, its high functional integration, reduced number of assembly steps and the improved reliability, for example regarding soldered connections [3, 4]. On the other hand, a significant challenge for direct packaging of electronic devices is the dissipation of excess heat, which may reach a considerable level especially in automotive applications. In a conventional housing, heat dissipation is often achieved by connecting to a cooling structure. Since plastics are generally thermally insulating materials, corresponding functionalization is necessary, for example by adding thermally conductive particles.

Filling in the case of thermosets is normally described by a so-called block-shear flow. This filling behavior is triggered, for example, by the thermal conditions and resulting viscosity profile: while the material in direct contact with the mold is heated very rapidly and the viscosity is reduced correspondingly, the viscosity in the interior is higher because of the lower temperature. Correspondingly, the material is strongly sheared, particularly in the peripheral region, resulting in a filler orientation induced by the flow. In the interior, a statistical orientation of the fillers is assumed. Based on studies with magnetic and thermally conductive fillers, it was possible to demonstrate this behavior for different sheet thicknesses (Fig. 1) [5, 6]. Thermally conductive fillers with a platelet shape, such as hexagonal boron nitride, also show a similar behavior. Small platelet thicknesses, in particular, show a pronounced orientation of the fillers in the flow direction, while with large platelet thicknesses, the thermal conductivity is highly pronounced in the z-direction.

There is only a limited range of thermally conductive materials available for use in thermoset molding compounds. Nevertheless, some commercial materials are available. The thermal conductivity of thermoset molding compounds extends from values in the range from 0.5 W/m·K (standard material) to 8 W/m·K (thermally conductive polymer). However, the measurement method used plays an important role. For the measurements in the present case, the test unit NanoFlash LFA447 from Netzsch-Gerätebau GmbH was used. A special sample preparation allows the thermal conductivity to be recorded in all spatial directions, which is of great importance for thermal simulations and for part design.

Power Loss and Thermal Conductivity not Proportional

In addition, the materials were checked for heat dissipation under free and forced convection, and special heat removal structures, such as pins and ribs were molded on directly in the injection molding process [7]. It was found that the recordable power loss does not rise in proportion to the thermal conductivity (Fig. 2). A high dosage of the fillers, which generally leads to a strong price rise of the materials, does not inevitably result in an improvement of the thermal conditions in the packaged device.

The process of direct packaging is normally included at the end of the value-creation chain. The requirements on feasibility and reproducibility of the process are therefore correspondingly high. An error occurring in the process, for example due to a pressure spike during filling as a result of fluctuations in the material or process, can damage the electronic components. Since, in addition, the molds are often multicavity for cost reasons, the monetary damage can very quickly become very high. Due to the absence of a non-return valve, special attention is therefore paid to reproducibility particularly during thermoset injection molding. Besides the use of materials with low viscosities to minimize the cavity pressures as far as possible, precise process control is also necessary.

To permit this, the cavity pressure was investigated at Bosch during packaging with various materials. Whereas standard material shows very low cavity pressures of about 10 bar, they are already significantly higher for the thermally conductive material (Fig. 3). The filling behavior is also very different. With standard material there is virtually no difference between the pressure measured close to and distant from the gate. Only a small pressure increase close to the gate during filling is noticeable. With the thermally conductive material, on the other hand, the pressure close to the gate increases strongly during filling, which is another sign of the material’s higher velocity. Although a slight improvement regarding thermal conductivity can be achieved by increasing the temperature of the insert, the mentioned pressure rise can already be clearly seen.

The effect of the cavity pressures and filling behavior can be very readily assessed from microsections of the packaged electronics. In the investigated case, the sensitive devices were represented by an SMD (surface-mounted device) and a THT (through-hole technology) electrolytic capacitor. Both components show signs of failure at cavity pressures over 50 bar. While in the case of the SMD electrolytic capacitor, a slight indentation of the housing can be seen, with the THT electrolytic capacitor, predominantly the rubber cap is pressed in. At even higher cavity pressures, complete failure of the device eventually occurs (Fig. 4).

Another fault pattern is caused by the viscosity of the materials and the resulting stresses during filling. This may result in displacement of the capacitor in the flow path direction (Fig. 5). The contacts are bent and the rubber cap is also pressed in. The filling step can thus lead to failure of the device. In addition, the mounting and connecting technology also includes even more sensitive devices such as bond wires, for which the permissible stresses are even lower.

Besides the difficulties in encapsulating electronic devices described above, there are also other challenges. They include, e. g., air inclusions in the component, delaminations between molding compound and device, deformations of the circuit board and solder point damage, as well as the necessary underfilling of components. Depending on the device and components, this list can be further extended. Good process control is therefore all the more important. However, a suitable method for designing the part and process is required.

The reproducibility of the material and process play a key role in the packaging of electronic devices. As mentioned above, electronic packaging is the last stage in a long process chain and the financial risks in the event of rejects are correspondingly high. Even minor changes in the processing properties or boundary conditions can have an influence on the process quality. It is essential to have a suitable strategy for material qualification as well as process control.

Differences between Simulation  and Reality

Besides real influences on the process and devices, virtual product development at Bosch is increasingly moving into the spotlight. To be able to minimize the above-described problems in advance, a correspondingly reliable process and structure simulation is necessary. Although filling simulation already provides very good results, e. g. as regards the filling behavior and occurrence of air inclusions and weld seams, quantitative evaluation still has room for improvement. Particularly as regards predicting process pressures during thermoset injection molding, some programs show clear differences between the measured values (Fig. 6). In addition, obtaining reliable material data is often a challenge for process simulation with thermosets.

In the example shown in Figure 6, the required pressure (specific hydraulic pressure) during mold filling has been underestimated for a good decade. The cavity pressure is also not correctly modeled by the simulation. Perfect pressure transmission appears to be present, which is not the case in reality. Other focuses in improving thermoset injection molding can be found in the area of the loads to be expected for fitted components and in predicting the lifetime of the packaged electronic components.

[1]  DRP 23 3803: Verfahren zur Herstellung von Kondensationsprodukten aus Phenolen und Formaldehyd (1908) Baekeland, L.H.

[2] J. Cederstrom und M. Walcher: Elko, Microcontroller & MOSFET – Prototypen und Lösungen für Serienumhüllungen, 10. Internationale Duroplasttagung, Iserlohn, 2019

[3]  M. Walcher: Duroplastisches Umspritzen von elektrischen Bauteilen mit Epoxid-Formmassen. Fuse Box meets dryer – Kunststoffe in E&E Anwendungen, Würzburg, 2018

[4]  H. Kawaguchi: Total SB solutions for lightweights in automotive. Lightweight composite solutions in Automotive (ICE, EV & Brakes) and other industries, Ghent, 2018

[5]  T. Maenz: Spritzgiesstechnische Herstellung duroplastgebundener Dauermagnete. Dissertation, TU Chemnitz, 2018

[6] T. Maenz, A. Jakobinski, G. Hülder, M. Gehde: On the filler orientation of functionalized thermoset molding compounds during injection molding. ANTEC, Anaheim, 2017

[7]  A. Jakobinski: Empirische Untersuchungen der Material- und Prozesseinflüsse beim Spritzgiessen wärmeleitfähiger Epoxidharze auf die Bauteileigenschaften. Masterarbeit, Hochschule Niederrhein, 2016

Robert Bosch GmbH CR/APP 

https://www.bosch.de

Ausgabenartikel

In direct packaging,  the electronic devices or components are directly overmolded with the molding compound 

Fig. 1. Thermal conductivity depending on the flow direction for different sheet thicknesses: with increasing sheet thickness, the thermal conductivity decreases in the x-direction and increases in the  z-direction 

Fig. 2. Thermal conductivity (left) and power consumption (right; with/without convection) for 2 mm thick sheets of different thermoset molding compounds: the thermal conductivity and power consumption of the materials increase disproportionately to one another

Fig. 3. Comparison of the cavity pressures for materials with lower (left) and higher (right) viscosity: at lower viscosity, the cavity pressure is significantly lower 

Fig. 4. Fault patterns in SMD and THT electrolytic capacitors: higher cavity pressures can lead to damage of the devices