Log In   |   Sign up

New User Registration

Article / Abstract Submission
Register here
Register
Press Release Submission
Register here
Register
coolingZONE Supplier
Register here
Register

Existing User


            Forgot your password
December 2005
library  >  Application Notes  >  Sarang Shidore

DELPHI Compact Models Revolutionize Thermal Design


by sarang shidore and dr. akbar sahrapour
flomerics inc.


abstract


the field of component-level thermal design has taken a giant step forward with the release of the delphi compact model capability by a leading software vendor. this study shows how delphi compact models are the method of choice for predicting the performance of ic packages in realistic electronics cooling environments.

 

although two-resistor models are useful in some design situations, the thermal community is already switching to the use of delphi compact models due to their greatly superior performance and computational efficiency.


background

 

the field of component modeling in thermal design tools has come a long way since studies in the early 1990's on creating validated detailed models by pioneering researchers such as harvey rosten of flomerics. however, before we talk about the latest advances in compact modeling in the thermal analysis world it is important to recall that there is a clear distinction between a detailed model and a compact model.

 

a detailed model is a model that attempts to represent or reconstruct the physical geometry of a package to the extent feasible. thus the detailed model will physically always look similar to the actual package geometry. a properly constructed detailed model is, almost by definition, boundary condition independent (bci); i.e. the model will predict the temperature of the various elements within the package (including junction, case, and leads) accurately regardless of the computational environment in which it is placed.

 

a compact model on the other hand is a behavioral, model, that aims to accurately predict the temperature of the package only at a few critical points - junction, case, and possibly leads. it cannot predict the temperature at any other part of the package. most importantly, a compact model is not constructed by trying to mimic the geometry and material properties of the actual component. it is rather an abstraction of the response of a component to various boundary conditions.

 

the challenge in the area of compact modeling is to come up with a generalized methodology to generate bci compact models. fortunately for the thermal design world, this problem has essentially been solved. in the 1996 the delphi consortium, made up of a number of primarily end-user companies (and also included one software vendor - flomerics), concluded a publicly funded ambitious research project that led to the first thorough methodology for the generation of bci compact models. this project was followed up by the seed project, in which component suppliers evaluated the delphi methodology (as it is known), and found that it works.

 

it is important to bear in mind that the delphi methodology is a non-proprietary, open methodology that is under active consideration by the jedec jc 15.1 committee on thermal phenomena as the framework for an industry-wide standard on compact modeling.

 

delphi compact models are made up of several thermal resistors that connect a junction node (representing the die) to several surface nodes. thermal links are also allowed between the surface nodes (shunt resistors). schematically, a delphi compact model looks like this (example applies to a leaded package):


figure 1: delphi compact model structure

 

a future article will focus on the theoretical details of the delphi methodology. meanwhile, let us see what the software industry offers to the designer in the way of bci compact models.


thermal design tools and compact modeling


when it comes to component modeling, the industry-standard thermal design tool flotherm pioneered the first parametric capability for the generation of detailed models when it introduced flopack in october 1998. flopack allowed the generation of standard jedec outline packages through its smartpart wizards. flopack allows the rapid generation of a component model at all levels - detailed, 2-resistor, and delphi.

 

the smartpart wizard interface means that a user can generate a component model with minimal information about the part, thus allowing its use by the end-user community. flopack now supports all the major ic package styles, sockets, pcb's, and heatsinks.

 

flomerics pioneered the generation of compact models with its release of two-resistor compact models in flopack during the summer of 1999. a few months ago, flomerics continued its trailblazing efforts in compact modeling by becoming the first and only tool to support the generation of bci delphi compact models.


example: 208-lead pqfp package


let us see how all this works out for a realistic problem. consider a common package, let's say a 208-lead pqfp (plastic quad flat pack), with a die size of 10 mm x 10 mm, and a heat dissipation of 2 watts. we will simulate the detailed, two-resistor, and delphi models under a number of typical electronics cooling environments, compare the results, and draw conclusions.


generating the two-resistor and delphi models


the two-resistor model is automatically generated within flopack by simulations in the appropriate jedec environments to extract theta-jc and theta-jb by a process invoked as soon as the user clicks on the appropriate button. the process is summarized in the flowchart in figure 2. the delphi models are generated based on the delphi approach, which has been described in detail in the literature.


figure 2: two-resistor model generation in flopack

 


the flopack smartpart wizard generates a detailed model of the package in a matter of seconds. once the detailed model is generated, the user has the option of generating either a two-resistor model or a delphi compact model. the generation of a compact model takes barely a few minutes.


once the model is generated, the user can download it and seamlessly import it into flotherm. the delphi model also generates an error estimate, which serves as a guide to the quality and expected performance of the compact model.

 

simulation results

 

the true test of a bci compact model is that it should give us acceptable errors in junction temperature results for a wide range of realistic environments.


accordingly, the detailed, two-resistor and delphi compact models were simulated in the following environments:


  • single, bare package in natural convection
  • single package with heatsink in natural convection
  • single, bare package in forced convection at 2 m/s
  • single, bare package under impingement flow (jet exit velocity of 1 m/s)
  • package with neighboring components at forced convection at 2 m/s

 


in each case the same pcb was used - a 4 layer (2s2p) pcb with a size of 100 mm x 100 mm. the ambient temperature for the natural convection environments was 30c and that for the forced convection environments 25c.

 

the simulations were conducted in the electronics thermal design tool, flotherm. in general the simulation time for the two-resistor and delphi compact models was at least five times less than comparable simulations with the detailed model.

 

the figures that follow give an idea of the environments chosen for this validation exercise, and some of the results obtained. figure 1 shows the temperature fills only for the two-resistor model under natural convection. figure 2 displays the temperature fills and velocity vectors for the detailed model in natural convection with attached heatsink.

figure 3: two-resistor model in natural convection (temperature fills only)

 

figure 4: detailed model with heatsink under natural convection

 

figure 5: delphi compact model under forced air at 2 m/s (temperature fills only)

 

figure 5 shows the temperature fills for the delphi model of the package under forced air at 2 m/s.


figure 6: detailed model under impinging jet at 1 m/s

 

figure 7: detailed model with neighboring components in forced air at 2 m/s



figures 4 and 5 show the vector and temperature fields for the detailed model for the last two environments - impingement flow, and board with neighboring components, respectively


the results for the junction temperature are tabulated in table 1. note that the temperatures are tabulated in c, and the errors in percentages. it is clear from this table that the two-resistor model exhibits a variable error trend, and in two out the five cases, slightly exceeds 30%. the errors for the junction temperature on the other hand are all within 10%, consistent with its bci nature.


environment
detailed
2-res.
delphi
error, 2-res.
error, delphi
natural
92.1
86.6
88.7
-8.9
-5.5
natural, heatsink
71.3
71
72.1
-0.7
1.9
2 m/s
72
57.8
67.8
-30.2
-8.9
1 m/s , impinging
75.2
64.6
73.2
-23.5
-4.4
2 m/s, components
77.1
62.3
72.6
-31.4
-9.6

table 1: junction temperature data (c) and errors (%) for the simulations


table 2 lists the results for the heat flux (in watts) flowing from the pqfp to the board. this is an important parameter, as the flux has the potential to influence the temperatures of neighboring components. here, the performance of the two-resistor model improves slightly, but the maximum error is still in the neighborhood of 25%.

 

the delphi model again agrees to within 10%, confirming that it is indeed boundary condition independent.

 


environment
detailed
2-res.
delphi
error, 2-res.
error, delphi
natural
1.77
1.59
1.71
-10.2
-3.4
natural, heatsink
1.47
1.1
1.42
-25.2
-3.4
2 m/s
1.26
1.05
1.2
-16.7
-4.8
1 m/s , impinging
1.4
1.17
1.32
-16.4
-5.7
2 m/s, components
1
0.93
1.04
-7.0
4.0

table 2: heat flux to the board data (w) and errors (%) for the simulations


conclusions

 

the results showed that the two-resistor model predicted the junction temperature and heat flux to the board to within approximately 30% in all cases, consistent with the results of a number of studies. this makes a two-resistor model useful for some limited design objectives; however errors of such a magnitude are not acceptable when accurate temperature predictions are required under challenging design constraints.

 

the delphi model, on the other hand, yields a better than 10% error for every environment examined for both the junction temperature and the heat flux. if we also keep in mind that the time savings realized by using the delphi model over the detailed model were a factor of five or more in each case, then the use of delphi models becomes irresistible.

 

as the pioneer among the software community in the field of electronics thermal design in general and component-level thermal analysis and design in particular, flomerics is pleased to have contributed to enhancing the productivity of mechanical designers through the release of boundary condition independent delphi compact models in flopack.


references

1. http://www.flomerics.com
2. http://www.flotherm.com
3. http://www.flopack.com

 



 

 

 

about sarang shidore:

 

sarang shidore obtained engineering degrees from iit madras (india), texas a & m university (college station), and university of texas (austin). he worked at flomerics inc. in various roles in engineering and product management with a special focus on package-level thermal modeling and analysis, a field in which he has authored several papers and articles.

 

in addition, he worked for mentor graphics as product marketing manager and for several years as a consultant for various organizations. he is currently a visiting scholar at the lbj school of public affairs at the university of texas focused on energy and climate policy and future strategies. 

Choose category and click GO to search for thermal solutions

 
 

Subscribe to Qpedia

a subscription to qpedia monthly thermal magazine from the media partner advanced thermal solutions, inc. (ats)  will give you the most comprehensive and up-to-date source of information about the thermal management of electronics

subscribe

Submit Article

if you have a technical article, and would like it to be published on coolingzone
please send your article in word format to [email protected] or upload it here

Subscribe to coolingZONE

Submit Press Release

if you have a press release and would like it to be published on coolingzone please upload your pr  here

Member Login

Supplier's Directory

Search coolingZONE's Supplier Directory
GO
become a coolingzone supplier

list your company in the coolingzone supplier directory

suppliers log in

Media Partner, Qpedia

qpedia_158_120






Heat Transfer Calculators