Chip-on-board in some applications represents the most cost effective way to incorporate low profile applications.
GLOB-TOP ENCAPSULANTS WITH PROVEN RECORDS OF LONG-TERM RELIABILITY
Besides outlining the B-stageable paste and preform lid-sealing adhesives that have been used extensively for cavity package protection for over 20 years, AIT also detailed the new generation of glob-top encapsulation compounds that have been proven in recent years for advanced microelectronics with high temperature and thermal dissipation performances. These AIT innovative products include:
- AIT glob-top encapsulants have ultra-high Tg of 175-240°C to suit the lead-free soldering processing
With the use of lead-free soldering, high temperature is exposed for components that have to pass through the soldering process along with other components on the same board. Besides having high moisture resistance and low moisture absorption to avoid “pop-corn” effect, higher Tg helps to minimize the tensile stress regime and thus more yield and end with more reliability.
- All of the AIT glob-top encapsulants also provide additional thermal dissipation capability in addition to mechanical protection and moisture barrier.
On the component level, glob-top encapsulation acts more like liquid molding compound with the provision of glob-top dam that can be build-in or using encapsulation dam materials.
GLOB-TOP MATERIALS FOR CHIP-ON-BOARD (COB) CHIP PROTECTION
WITH SECOND GENERATION OF MODIFIED EPOXY COMPOUNDS
Traditional underfill and glob-top materials with anhydride curng epoxies have Tg around 100-150°C that may exert too high interfacial tensile stress when going through reflow soldering at 250°C. A new generation of AIT underfill and glob-top compounds with different chemistry enables a new paradigm of performance in ultra high Tg of 240°C and incorporating high thermal conductivity and low thermal interface resistance to power the transfer of heats from both the top and bottom sides of the flip-chip packages. Please CLICK HERE TO VIEW VIDEO for details of AI Technology’s Underfill And Glob-Top Encapsulant Products in enabling higher performance flip-chip and chip-on-board devices.
Properties of Lid-Seal Adhesives and Glob-Top Encapsulants
| PROPERTY | MC7865-GT (Glob-Top Encapsulant) | MC7685-GTS(Glob-Top Encapsulant) | LESP7670-HF (ESP7670-HF) (Lid-Sealing) | LRTK7660-HF (RTK7660-HF) (Lid-Sealing) |
| Electrical Resistivity | >2X1014 Ω-cm | >2X1014 Ω-cm | >5X1014 Ω-cm | >2X1015 Ω-cm |
| Viscosity @5.0 rpm /Thixotropic Index | 60,000 cps/2.5 | 60,000 cps/2.5 | 65,000 cps/4.0 | 65,000 cps/4.0 |
| Material Form Factors | Syringe and Frozen Storage | Syringe and Frozen Storage | B-Stageable at 50-70°C to dry preform | B-Stageable at 50-70°C to tacky preform |
| Customizable Parameters | Viscosity and Thixotropic Index | Viscosity and Thixotropic Index | Conductive and/or Thermally Conductive | Conductive and/or Thermally Conductive |
| Glass Transition Tg (°C) | 240 | 175 | 130 | 165 |
| Device Push-off Strength (psi) | >3500 | >4000 | >3000 | >4000 |
| Hardness (Type) | ~ 90D | ~ 90D | ~ 90D | ~ 85D |
| Cured Density of Conductive Adhesive Portion (gm/cc) | 2.5 | 2.5 | 1.6 | 1.6 |
| Thermal Conductivity | > 2.0 W/m-°K | > 1.8 W/m-°K | > 0.20 W/m-°K | > 0.20 W/m-°K |
| Thermal Expansion Coefficient (ppm/°C) | 18 (X-Y=Z, Isotropic) | 19 (X-Y=Z, Isotropic) | 35 (X-Y=Z, Isotropic) | 35 (X-Y=Z, Isotropic) |
| Maximum Continuous Operation Temperature (°C) | > 250 | > 200 | 150 | 150 |
| Decomposition Temperature @5% weight loss (°C) | >450 | >450 | >450 | >450 |
| Recommended Curing Temperature/Time (°C/min.) | >125/60 | >125/120 | >150/30 | >150/30 |
With the additional dimension of adding high thermal conductivity and low interfacial thermal resistance in the underfill and glob-top compounds, thermal dissipation of components generating heat can be assisted with thermal slug and in case of underfill material for the flip-chip components, heat can be dissipated via the provision at the front side of the flip-chip in additional to the traditional backside of the chip.
For more information and recommendation assistance, please contact AIT sales and engineering:
AIT technical sales and service department can also be reached at: 1-609-799-9388 or 1-800-735-5040 (EST) and Fax: 609-799-9308