Self-adhesive spacer tapes help bonding of slim mobile phones

Paul Boughton

Christina Barg-Becker looks at bonding technology being used in slim phones.

Mobile phones these days are not just a multi-media communication tool, they also represent status and excellent taste. Next to the increasing complexity of its electronic parts new designs play a decisive role.

Due to this development the connecting components in such devices must meet many new different challenges. This includes, for example, the trend towards thinner products, like so-called slim phones, which is continuing today, and calls for an innovative bonding technology. Double-sided pressure sensitive spacer tapes as die-cuts are an adequate new solution because they meet the various requirements of this special industry.

Die-cuts consisting of single and double-sided pressure-sensitive-adhesive tapes, with laminates or special foams, membranes and films are used in many industries. For example, for medical applications, as diagnostics or for the electronic-, automotive- and mobile communication industry.

Lohmann, with its die-cutting competence centre and long lasting experience in creating customised adhesive tapes, has a solution. A wide range of different pressure sensitive adhesive applications are being used in a mobile phone. For example, fixation of the icon or front plate, dust protection of display and microphone, fixation of flexible antenna, heat management and EMI Shields. But even apparently simple die-cuts, such as the protective film for mobile phone displays, require utmost care with regard to contamination with even the smallest dirt particles. This means they have to be produced in a clean-room. In a cleanroom the cleanliness of the air is achieved by sophisticated high-volume HVAC systems with multiple step filters (positive pressure ventilation), by appropriate clean room garments and by closely monitored working procedures. Precision die-cuts in the micron range feature a multitude of design advantages. They are not only available in virtually any conceivable shape and size, they also offer ease of assembly, greater process flexibility and secure high volume production. Die-cuts separate and protect different material layers and achieve corrosion-free joints without screws or rivets.

Concerning the special mobile communication industry nowadays, the market activities are focused on Asia. In close collaboration with the German headquarters Lohmann's subsidiary in China is continuously creating new customised solutions locally. The latest result is a new product range for slim mobile phones. With the customised DuploCOLL spacer tapes the company has created a new range of high-tech die-cuts to fit process-designed-specifications. They not only fulfill the requirements of reducing weight and space but also meet further challenges. For example, despite the smaller bonding areas, the die-cuts have to perform in their usual way. This means, for example, a high adhesion for permanent fixings, high resistance to plasticisers or a secure bond at elevated temperatures. By using DuploCOLL spacer tapes, the number of bonding components in a mobile phone is reduced and the total thickness of the construction is decreased. And this means an absolute advantage for the customer, allowing more freedom of design.

Looking at the cross section of a conventional mobile phone in short, it is built up in the usual way. All electronic components are situated between the so-called A- and B-cover.

They are bonded in the following way: LCD-panel, a pressure sensitive foam die-cut, the plastic bar and a pressure sensitive die-cut to fix the lens. Therefore the total thickness between the lens and the display averages from 0.5 to 1 mm, which depends on the multi-layer construction.

New slim phones show a different cross section; all electronic parts lay in the B-cover with an upper panel above. This means that the A cover is no longer required and the construction is: LCD panel, spacer tape die-cut, lens. With the new spacer tapes the window lens is mounted directly on to the LCD panel and the conventional construction is simplified, which saves weight and space.

Furthermore, the new spacer tapes which connect the lens directly to the core, are waterproof and shock absorbing. The DuploCOLL spacer tapes product range is available in six different tapes which differ in color and performance. For example, black 'spacer tapes' are developed in order to absorb the diffused light, while others are transparent, due to design requirements.

Spacer tapes with an additional feature can be offered too. For example, when the compensation of tension stress is an important feature. For this special application spacer tapes can also be produced as very thin PE-foam die-cuts between 250 and 350 microns. Even here, these foam spacer tapes connect the lens directly with the display. Last but not least all these customised spacer tape utilise high performance with narrow tolerances, constant release properties and are cleanroom qualified. This enables customers to set up a less-sensitive, assembly line for high volume production, which is highly cost efficient.

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Christina Barg-Becker is with Lohmann GmbH & Co KG, Neuwied, Germany. www.Lohmann-Tapes.com

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