Hello and welcome to another polymer material selection example for which we use the POMS-Funnel Method (in detail explained here and in this video). Today’s mission is to select the optimal polymer for Liquid Crystal Display (LCD) bezel used in smartphones.
Figure 1 presents the four different stages of the material selection funnel as well as the tools we can use to facilitate the selection. We can use this as a guideline throughout the selection journey.
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| Figure 1: Polymer Selection Funnel - overview of the four different funnel stages and tools. |
POMS-Funnel Method:
Funnel stage 1: Material selection factors
In the first Funnel stage we focus on gathering and understanding all the requirements of the LCD bezel for smartphones (Figure 2).
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| Figure 2: Overview of a LCD front bezel used in the iPhone 14 Plus. Aim of the first funnel step is to lay out the requirements. |
Covering effectively the product requirements, a combination of functionality questions and selection factor questions can support you to achieve this. First we have to ask some questions on the functionality of the part.
Following questions can help us with this assessment:
-What are the performance requirements (structural, etc.)?
-Do you want to combine multiple parts or functions?
-What will be the structural load of the part (static, dynamic, cycling, impact, etc.)?
-What will be the environmental impact on the part (chemical, temperature, time)?
-What is the expected lifetime of the product?
After answering the functionality questions, we continue with the, in my point of view, six essential questions on material selection factors (6 What's).
A more detailed list can be found here (incl. download): Material Selection Requirements Checklist
1. What is the service environment of your part?
2. What are the regulatory requirements?
3. What types of load at which service temperature and time need to be fulfilled?
4. What other things such as wear and friction, electrical properties such as CTI, electrical breakdown strength, aesthetics and colour (relevant for application with food contact, and toys), and more, need to be considered?
5. What is the processing and fabrication method?
6. What are the economic and commercial considerations?
In general, LCD bezels, the outer frame that surrounds the LCD screen in smartphones, play a crucial role in both aesthetics and functionality. The materials used for these bezels must meet specific requirements to ensure optimal performance and durability.
Key Requirements for LCD Bezel Materials:
Aesthetics:
-Color: The bezel's color should complement the overall design of the smartphone and align with current trends.
-Finish: The finish can range from matte to glossy, depending on the desired aesthetic.
Texture: The texture can be smooth, textured, or even embossed to create a unique feel.
Durability:
-Scratch Resistance: The material should be resistant to scratches, as smartphones are often carried in pockets or bags and may come into contact with other objects.
-Impact Resistance: The bezel should be able to withstand minor impacts without cracking or shattering.
-Strength: Thin wall frame need to have high strength levels too, together with dimensional stability.
-Wear and Tear: The material should be durable enough to resist wear and tear over time.
Functionality:
-Signal Transmission: The bezel material should not interfere with wireless signal transmission, such as Wi-Fi or cellular data. The material should have a dielectric constant of 3.5.
-Display Visibility: The bezel should not obstruct the viewing angle of the LCD screen.
-Thermal Conductivity: The material should have good thermal conductivity to help dissipate heat generated by the smartphone's internal components.
-Processability: High flow material enabling to fill thin wall thickness; possibility for IML/IMD “In-Mold Labelling/Decoration”,
Cost:
-Affordability: The material should be cost-effective to ensure that the smartphone remains competitive in the market.
Capturing all requirements and project details can be done by using the requirement worksheet and Table 1 shows the outcome.
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| Table 1: Overview of requirements for the LCD front bezel using the requirement worksheet. |
Funnel stage 2: Decision on thermoplastic or thermoset
With the LCD bezel requirements, together with the understanding of the differences of thermoplastics (amorphous and semi-crystalline) and thermosets we can screen the databases and material suppliers for suitable material candidates.
There are reliable database such as Campus and Omnexus and I created dashboards to support this step too:
All dashboards can be found also here.
Deciding between the thermoplastic or thermoset route is the first step. In our case, thermoplastics offer many advantages for this application, especially impact performance at low and high temperatures and injection moulding in the range of million parts per year in an economical way. Reviewing the bezel requirements, both amorphous and semi-crystalline materials are feasible.
After the material screening, I pre-selected the following materials (Table 2):
- Lexan® HFD4472 (PC-CoPo-GF20)
- Kalix 2545 (PA 6.10-GF45; bio-sourced)
- TORAYCON™ 7151G-F03 (PBT+SAN-GF30)
- Zytel® HTN52G35HSL (PPA-GF35; PA6T/66-GF35)
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| Table 2: Overview preselected grades and their commercial suppliers. |
Funnel stage 3: Selection discussion with worksheet (qualitative matrix analysis)
The third funnel stage represents a core element in the whole material selection funnel. It is a detailed selection discussion with a worksheet. I call it the decision matrix analysis and it ranks all of the pre-selected polymers. The decision matrix analysis consists of five steps. The base calculation principle is a scoring of each of the pre-selected materials for each of the material selection factors. In the end we add up all weighted scores for each material. The materials with the highest score are most suitable for selection and further investigation in the fourth stage.
How to start the qualitative matrix analysis?
I developed an online tool in order to facilitate this step here (Polymer Material Selector V1.1). As an alternative, you can reach out to me and I will provide you with an excel version of it. I only considered the must-have requirements.
In Table 3 the outcome of the qualitative matrix analysis is shown. PA 6.10-GF45 scored the highest number of points (score: 132 points), followed by PC-CoPo-GF20 (score: 98 points) and PBT+SAN-GF30 (score: 97 points) and PPA-GF35 (score: 93). All four materials should be validated in the Funnel stage 4 since there are important tests such as the antenna performance tests, falling and rolling test, and anti-stain test.
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| Table 3: Results of the qualitative matrix analysis. |
Funnel stage 4: Testing, selection of material and vendor
In the final step of the POMS-method we perform the antenna performance tests, falling and rolling test, and anti-stain test, as well as build first prototypes (with the support of CAE - filling simulation). Once all the test results are available, the final material decision can be done.
For the premium consumer segment of smartphones, PA6.10-GF45 and PC-CoPo-GF20 are a good choice and if surface aspects are not the most important criteria, the remaining two materials (PPA and PBT+SAN) can be considered too.
Conclusions
In this example we applied the POMS-method for selecting the optimal thermoplastic grade for a LCD bezel used in smartphones. It is a systematic approach with a resin-agnostic view allowing to consider different material choices and document them for a later review and optimization.
More polymer material selection examples using the funnel approach can be found here:
Thanks for reading and #findoutaboutplastics
Greetings
Herwig Juster
Interested in my monthly blog posts – then subscribe here and receive my high performance polymers knowledge matrix.
Literature:
1] https://www.sunsky-online.com/de/p/EDA006095301/For-iPhone-15-Plus-Front-LCD-Screen-Bezel-Frame.htm
[2] https://www.polymerio.com/tds-pds/pbt-compound-toray-toraycon-7151g-f03-b--tds-pds
[3] https://materials.celanese.com/de/products/datasheet/SI/Zytel%20HTN52G35HSL%20BK083
[4] https://www.syensqo.com/en/brands/kalix-hppa
[5] https://www.sabic.com/en/products/specialties/lnp-compounds-and-pc-copolymer-resins/lexan-copolymer
[6] https://www.plastics.toray/de/products/toraycon/pbt_003.html
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