PCB Blog - How to establish an accurate IC packaging model?

How to build an accurate IC package model is the key problem and challenge of electronic component level and system level thermal simulation. It is important for the thermal design of electronic products to establish an accurate and effective IC packaging model. For board level or system level simulation containing a large number of IC package, it is more important to improve the modeling speed of IC package. A convenient and fast model library is needed to improve the timeliness of tasks and save computing resources. The next two articles will briefly discuss the types of IC packaging models commonly used in engineering, and introduce the IC package modeling methods in Simcenter Flotherm.

IC packaging modeling is mainly divided into two categories: Detailed Thermal Model (DTM) and Compact Thermal Model (CTM).

one point one

Detailed modeling DTMDTM is to use simulation tools to imitate and copy the actual physical structure and materials of IC packaging as specifically as possible, usually combined with the CAD model of IC packaging. Therefore, from the appearance, DTM is always similar to the actual IC package. However, the detailed model will also appropriately simplify the components in the package according to the requirements of the studied problems, such as replacing the BGA solder ball array with a cube with consistent overall size, replacing the actual substrate routing with a substrate with a given copper content, and so on. The combination of measurement tools and simulation tools can also calibrate DTM, reducing the error between DTM structure function and actual package structure function to less than 3%. The second section of this article will further discuss Simcenter Flotherm's model calibration function.

DTM has high accuracy and is independent of boundary conditions. It is often used for chip or package design and manufacturing, such as typical package parameter characterization, package design optimization, etc. However, due to the large difference in the size of components inside IC packages, DTM will generate too large a grid, reducing the simulation efficiency. Therefore, for board level simulation, it is recommended that only important packages be modeled in detail, while system level or above simulation, because it contains a large number of packages, usually does not use DTM, but uses CTM description.

one point two

Compact Modeling CTMCTM is a behavioral model that does not model the actual physical structure or materials of IC packages, but rather simulates the thermodynamic response of IC packages to the environment. It aims to accurately predict the temperature of several key locations (such as nodes, shells, and leads), usually in the form of a thermal resistance heat capacity network.

The two most commonly used CTMs are the dual thermal resistance (2R) model and the DELPHI model. The 2R model is the simplest and the most widely used. Its structure is shown in the figure below, including three nodes: junction, case, and board θ JC (junction to case) and θ JB (junction to board) two thermal resistances. The JEDEC related standards define the measurement method, which can be referred to.

The advantage of 2R model is that its structure is simple and clear, and the thermal resistance can be measured through experiments, so it is widely used in board level or system level modeling of multiple packages; However, its construction method determines that the error of 2R model under specific working conditions cannot be calculated in advance. 

Considering the advantages and disadvantages of 2R model, it is recommended to use 2R model to roughly predict junction temperature at the initial stage of design. In the later stage of design, 2R model is more suitable for parameter comparison analysis than specific temperature/heat flow prediction.

In recent years, more and more suppliers have started to provide DELPHI models for IC package products to facilitate users' thermal simulation analysis, and the popularity of DELPHI models is increasing. Some electronic thermal simulation software tools, such as Simcenter Flotherm, also provide a large number of templates for users to easily and quickly establish DELPHI models and other CTMs or DTMs. Next, IC package this article will introduce the methods of building various thermal models in Simcenter Flotherm.