Preparation

Preparation Work Flow

The preparation is carried out in the following four stages.

Design

The first stage of preparation is a detailed assessment of the intended application of the die and package or PCB board. Their operational conditions in terms of temperature, chemical exposure and mechanical stability are considered. The tolerances of the individual components and the whole system is considered to determine the maximum temperature, chemical exposure limits and suitable processing environment. The physical size of the die and package/PCB is acquired to evaluate the encapsulation requirements. Some applications may require the encapsulation process to be simulated before it is carried out.

Simulations can help determine the optimum material characteristics for a specific die, interconnect and package/PCB. These simulations are carried out in finite element analysis software such as Autodesk and COMSOL using analytical models of the die, interconnect and packaging/PCB arrangements.

Material Selection

The second stage is to shortlist encapsulants which are compatible with the die, electrical interconnections and package / PCB. The material selection takes in to consideration the main purpose of the encapsulation in conjunction with the operational conditions and tolerances of the die and package/PCB. They are often determined by the application requirements of the electronics to be encapsulated.

The materials are chosen so their processing and curing requirements fall within the tolerances of the die, interconnections, package and/or PCB boards. The characteristics of the encapsulants such as rheology, viscosity, transparency and colour are also important factors in selection of suitable materials.

Material Management

Once a material is selected, it requires appropriate storage and transport arrangements to avoid any potential damage to its physical and chemical properties. Some materials have very specific requirements for storage and transport such as low temperatures and UV sensitivity. Encapsulants have different pot lives which is the maximum amount of time they can be stored; an encapsulant should not be used after the expiry of its pot life.

Material Conditioning

Material conditioning deals with immediate preparation of the encapsulants for dispensing. This preparation is specific to material composition and requirements.

Encapsulation materials may consist of two parts which require mixing in specific proportions. Some encapsulants once mixed are prone to material separation after a certain amount of time. They can require regular mixing to ensure consistent dispensing.

Some two part encapsulants can start curing immediately when they are mixed and often have a window of three to four hours where their rheology is consistent and reliable for dispensing.

Encapsulation Preparation at our Facility

The Advanced Packaging Facility has a range of material preparation and storage facilities. It has access to a dedicated material preparation facility which has a wide range of relevant equipment such as viscometers, speed mixer (centrifuge), vacuum chamber and mass scales. The materials preparation facility is located close to the packaging facility which helps avoid any significant time delay.

In terms of storage the packaging facility has a freezer which can store the materials down to -40°C and chemical cabinets which can store the materials at room temperature; the chemical cabinets are opaque so they offer protection against UV light. The facility also holds UV blocking containers for UV sensitive materials.

The packaging facility has access to a range of finite element analysis software such as Autodesk, ANSYS and COMSOL. We also have the relevant expertise to be able to comprehensively analyse a die to be encapsulated.