Hmmm…
If you’re guessing it’s a chip package, you’re right – got it in one. Well done!
OK, so what type of package is it?
If you’re thinking it’s a silly question as you don’t know anything about the package, other than I’ve told you its black – that was a hint that it’s an encapsulated plastic part by the way – you’d be right.
You’d need me to tell you if it had leads, and if so on how many sides – one, two or four, and if so whether it has a metal tab. If not, you’d need me to tell you if there are solder balls underneath it, etc. This is like a parody of the ‘guess the animal’ games that operators, bored of writing JCL to run payroll jobs, wrote for the early mainframe computers of the 1960s. Knowing the package is rectangular and has leads on the two longest sides doesn’t exactly nail it down – so it’s not like knowing the animal has a trunk! More importantly it doesn’t tell you anything about its internals, like whether it has a drop-in heat slug.
Unfortunately there’s quite a bit of subtle variation in IC packaging. Wikipedia has quite a long list of these.
We encountered this issue many years back, when customers first started performing detailed thermal simulations on PCBs and wanted to model the packages explicitly in order to predict case or junction temperature. We realized pretty quickly that we needed to help customers to build package thermal models or risk this limiting the use of our tools.
To address this we started an internal research project, titled (rather unimaginatively) our Package-Level Thermal Initiative. A number of customers got involved and the effort evolved into in a 3-year EU-funded collaborative research project called DELPHI, that went on to develop a new approach to modeling chip packages – compact thermal models, or CTMs. These modeling methodologies are now standardized by JEDEC, and the 2 Resistor and DELPHI guidelines are available to all:
JEDEC Standard: Two-Resistor Compact Thermal Model Guideline, JESD15-3, July 2008
JEDEC Standard: DELPHI Compact Thermal Model Guideline, JESD15-4, October 2008
Next time I’ll tell you how FloTHERM.PACK, which evolved as a product from the DELPHI project, can really help your thermal modelling by helping you build accurate thermal models of chip packages.
Dr. J, Hampton Court
