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With multiple stack chips and proximity of wire-bonding with sub-mil (<25 microns) gold wire and sub-mil spacing, these type of chip scale packaging requires new type of moulding compound to form its protections. Traditional epoxy moulding compounds requires high pressure and thus high swiping forces on these gold-wire bonding.
The ideal "new generation" of the chip packaging encapsulation includes all of the moulding compound characteristics that are part of the material properties of the innovative material design and engineering:
Low pressure moulding parameter similar to thermoset moulding that is 1/10 or less than traditional epoxy moulding compounds Much less moisture absorption and permeation than traditional moulding compound Coefficient of expansion (CTE) of less than 20 ppm/°C or lower than traditional epoxy moulding compound Higher glass transition temperature (Tg) or softening temperature Much higher modulus than traditional moulding compound to provide stable stress reduction due to CTE differences
The following are a list of the "new generation" of low pressure molding compounds and encapsulations from the material scientists from AI Technology, Inc.
Low Pressure Molding Compounds And Encapsulations
| AIT Part # | Description | Melt-Flow, Curing, Process Conditions | Modulus (GPa) | CTE (ppm/°C) | Tg (°C) | Dielectric Constant/Loss (1MHz) | Ionic Impurities (Na+, K+, Cl-, etc.) |
|---|---|---|---|---|---|---|---|
| MC9883-LPM | Quartz filled Semi-solid mixture Ultra low CTE | Injection or transfer @40-60°C Curing @ 175°C/10 sec | 8.0 | 16 | 236 | 3.8/0.01 | < 10 ppm |
| MC9885-LPM | Alumina filled Semi-solid mixture Thermally conductive | Injection or transfer @40-60°C Curing @ 175°C/10 sec | 8.0 | 18 | 236 | 4.2/0.01 | < 10 ppm |
Application Notes:
Low pressure moulding compounds and encapsulations are designed to have strong adhesion to most substrates used in electronic applications. All moulding surfaces in contact with the curing encapsulations and moulding compounds must be coated with release coating such as PTFE or silicone for releasing for multiple uses.
Low pressure moulding compounds and encapsulations are premixed, de-aerated (degassed) and ready for moulding without further mixing. Transfer of the moulding compounds and encapsulations is to performed at temperature below 60°C to ensure long processing time without curing at the transferring chambers.
Flip Chip Interconnections
For the traditional flip-chip underfilling, anhydride based epoxy encapsulation have been successful at least to meet the the JEDEC/IPC level 3 of moisture sensitivity. To meet the more stringent level 1 or 2 moisture sensitivity, the underfills must absorb much less moisture to reduce the potential moisture-induced failure.
More stringent stress management and reduction of moisture sensitivity are more important in the stack chip applications such as "through silicon vias" (TSV) interconnected stack chip packages.
AI Technology material scientists have developed a series of new generation underfills that withstand RoHS compliant higher temperature processing and applications. The main advanced features and functions are listed below alone with the table of characteristics:
Much lower moisture absorption and sensitivity than traditional epoxy underfills Lower and faster curing at relatively low temperatures of 150°C Higher Tg and modulus to enhance stress reduction Lower ionic impurities for even higher device reliability
High Temperature Underfills
| AIT Part # | Description | Capillary-Flow, Curing, Process Conditions | Modulus (GPa) | CTE (ppm/°C) | Tg (°C) | Dielectric Constant/Loss (1MHz) | Ionic Impurities (Na+, K+, Cl-, etc.) |
|---|---|---|---|---|---|---|---|
| MC7883-UF | Quartz filled Liquidous mixture Ultra low CTE | Capillary flow @40-80°C Curing @ 150°C/90 sec | 7.5 | 19 | 236 | 3.8/0.01 | < 10 ppm |
| MC7885-UF | Alumina filled Liquidous mixture Thermally conductive | Capillary flow @40-80°C Curing @ 150°C/90 sec | 7.5 | 20 | 236 | 4.2/0.01 | < 10 ppm |
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