Insights From Leading Edge



IFTLE 106 2012 Symp on Polymers for Microelectronics

This was the 15th year that polymer suppliers and users have met in Wilmington DE to discuss the latest advances in polymeric materials. All of the big boys were there including : HD MicroSystems , Dow, JSR, Asahi Kasei, Toray, Nippon Kayaku (MicroChem), AZ and Hitachi Chemical.

Certainly the most interesting bit of information that I learned about a materials supplier was that Alpha started its business in 1704 making cannon balls… cannon balls to solder balls – now that’s a roadmap for miniaturization!

Certainly the main theme, as you shall see below, was the development of low curing temperature polymers that could come close to matching epoxies curing temp (i.e ~175C) while maintaining improved thermal and mechanical properties.   

My plenary presentation was based on the new Yole report "PolymericMaterials for 3DIC & WLP Applications"

Basically over the last 50 years the industry has developed five  basic chemistries for the microelectronics industry. In chronological order they would be epoxies, siloxanes, polyimides, BCBs and PBOs.

(Click on any of the images below to enlarge them.)

If we look at the properties that are important to all or most functions / applications we find 4 broad categories including electrical, mechanical, thermal and misc. (other).

The half dozen key functions that we want these polymers to fill and the seven wafer level applications that we are looking to use them in are depicted below.


Yole projects a 26% CAGR for WL applications over the next few years which will expand the current market to near $1B with significant expansion of applications other than FC bumping.
Since new materials take decades and 10s of millions of dollars to develop, those in the business of wafer level packaging over the next 5-6 years will basically have products from these 5 chemistries to serve the functions for the listed applications.  

The theme for permanent dielectric suppliers at this meeting seemed to be positive tone aqueous developable dielectrics with sub 200C curing temperatures and resultant low stress. The newer packaging scheme such as eWLB require this evolution in dielectric materials because the wafer substrate is epoxy based and  cannot survive the processing temperatures needed to cure polyimides or most PBO and BCB materials. Also, ICs with embedded memory are very sensitive to process temperatures and survivability drops dramatically with increase in temperatures. Lastly, advanced technology nodes such as 32 and 22 nm use lower-k dielectric materials, which are sensitive to the high stresses generated by higher curing temperatures.
Toray is offering a LT series low-temperature curing,  positive-tone photosensitive PI coating with a 170- 200C curing temp and resultant 13 MPa thermal stress. With a tensile strength = 100 MPA, elongation of 30% and Modulus of 2.5 GPa . While the residual stress is reported as 13 MPa, the CTE is troubling at 70 ppm. Asahi Kasei is offering  BM series PIs which reportedly can cure as low as 200C with a Tg of 220C, a CTE of "50-60" and a stress of 19 MPa . HD Micro reported on a new PBO, 8850, with reported better chemical resistance, which can be cured at 250C. JSR reported on their WPR series dielectrics which for positive tone are cresol based with rubber reinforcement. While they can be cured at 200C and have low residual stress ( 20 MPa), their tensile strength (80 MPa) and elongation (7%) are low for permanent dielectrics.  Dow chemical reported on their aqueous developable P6505 BCB which cures as low as 180C (3 hrs) with a resultant stress of 25 MPa. Most of the properties look like the BCB 4000 series with a notable exception that water absorption has risen from 0.2% to 2% for the new version. 
Toray also introduced a siloxane product to replace acrylics for optical applications such as CMOS image sensors, LCD and OLED displays and solar modules. It is 99% transparent at 400 nm and is much more thermally stable than the typical acrylics.
As a general comment, all of these materials are beginning to look like one another which may or may not be a good thing for the industry. As IFTLE has said many times before, you must determine what properties are most important for your application and choose your dielectric accordingly. 
Next week we begin our coverage of the ECTC conference. For all the latest in 3DIC and advanced packaging stay linked to IFTLE………………….


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