High performance underfills development - materials, processes, and reliability

Nguyen, Luu; Hoang, Luu; Fine, P.; Shi, Shengjun; Vincent, Michael; Wang, L.; Wong, C.P.; Tong, Q.K.; Ma, B.; Humphreys, R. R.; Savoca, A.

doi:10.1109/pep.1997.656503

Cited by 42 publications

(9 citation statements)

References 7 publications

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“…The characterized material properties of the developed tacky material are listed in Table I. Since several separate papers have been published on the development of the no-flow underfill materials [6]- [10], this paper mainly involves the development of WLCFU material. Fig.…”

Section: A Materials Properties Characterizationmentioning

confidence: 99%

“…The conventional underfill technology has relied on capillary flow and has been developed and practiced for some time [6]; however, this conventional underfill technology needs separate flux dispensing, solder bump reflow, flux cleaning, underfill dispensing and flow, and off-line underfill curing steps. As such, the conventional underfilling process is tedious, expensive, and not transparent to the SMT facility.…”

Section: Introductionmentioning

confidence: 99%

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Development of the wafer level compressive-flow underfill process and its involved materials

Shi

Yamashita

Wong

1999

IEEE Trans. Electron. Packag. Manufact.

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This paper describes a wafer level compressiveflow underfill process for a novel SMT transparent flip-chip technology. In this flip-chip technology, a liquid fluxable wafer level compressive-flow underfill (WLCFU) material is first coated on the active side of an entire patterned and bumped wafer. The WLCFU layer is dried at an elevated temperature to form a solid layer. The coated bumped wafer is then diced into individual chips, which are then placed on a carrier film with their active side to the tacky side of the carrier film. These diced individual chips are then picked from the tacky carrier film and placed on a substrate such as a PWB board using standard SMT equipment. At an elevated temperature (100-180 C) during solder reflow, the solid WLCFU layer can be re-melted and can easily fill in the gaps between chip and substrate. After solder reflow (190)(191)(192)(193)(194)(195)(196)(197)(198)(199)(200) C ), the WLCFU material can be fully cured. A B-stage epoxy technology is used to develop this WLCFU material and the tacky material on the carrier film. A properly selected fluxing agent is added to both the WLCFU and the tacky materials to provide sufficient fluxing capability for good solder interconnection. A thermo-gravimetrical analyzer (TGA) is used to investigate the drying kinetics and the material weight loss during the reflow process. Differential Scanning Calorimetry (DSC) is used to study the curing kinetics of the prepared formulations. A thermo-mechanical analyzer (TMA) is used to investigate the heat distortion temperature (TMA Tg) and the coefficient of thermal expansion (CTE). A dynamic-mechanical analyzer (DMA) is usedto measure the storage modulus (E 0 ) and cross-linking density () of the cured materials. A rheometer is used to investigate viscosity () change with the temperature increase during the solder reflow process. Preliminary results demonstrate the feasibility of the proposed novel flip-chip technology with the developed WLCFU and tacky materials. The basic qualifications of the WLCFU material are examined. Some technical barriers related to this technology are also discussed.Index Terms-B-stage, compressive-flow, epoxy resin, underfill encapsulant, wafer level packaging.

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Section: A Materials Properties Characterizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Development of the wafer level compressive-flow underfill process and its involved materials

Shi

Yamashita

Wong

1999

IEEE Trans. Electron. Packag. Manufact.

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“…A useful no-flow underfill material has been developed in our lab [7]- [9]. One of the critical requirements for a useful no-flow underfill encapsulant is to provide enough fluxing capability during solder bump reflow.…”

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confidence: 99%

Study on the relationship between the surface composition of copper pads and no-flow underfill fluxing capability

Shi

Wong

1999

IEEE Trans. Electron. Packag. Manufact.

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The purpose of this paper is to investigate the effect of copper pad surface composition on the wetting of solder bumps during reflow process for a certain no-flow underfill material. A purchased copper foil which is laminated on FR4 board is used as a control surface. Six different procedures are followed to prepare the surface of the copper foil with six different compositions. The XPS is then used to analyze the surface compositions of the six surfaces and the control surface. An in-house developed G25 noflow underfill encapsulant is used to examine the wetting status of eutectic solder balls on these copper surfaces. The correlation of the copper surface compositions with the solder wetting is then established. It is verified that the compositions of the copper foil surfaces strongly depend on the cleaning procedures. For G25 no-flow underfill material, copper oxide (CuO) is the main composition that prevents the solder ball from wetting the copper foils while the observed organic contamination does not have noticeable effect on the solder wetting.

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“…While most of the parameters may be found or deduced, the surface tension in particular is difficult to quantify for a particular Underfill and surface. Equation (9) does, however, allow us to estimate the value of A where; (10) ...................…”

Section: Analysis and Discussionmentioning

confidence: 99%

Rheology of the underfill flow process in a flip chip package

Rasiah¹

Twenty Sixth IEEE/CPMT International Electronics Manufacturing Technology Symposium (Cat. No.00CH37146)

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Underfills that flow have traditionally shown superior reliability performance when compared to "No-flow" Underfills. This has ensured the necessity for "flowable" Underfills in the IC market particularly for microprocessors and other high performance chips. The speed of flow has been an issue in the industry. Faster flow would reduce cycle time, however, this should not be at the expense of reliability performance of the package. Schwiebert and Leong established the basic theory of the Underfill flow. Other authors have modified this with varying degrees of success, but in all these models the effect of the change in the Underfill viscosity during the flow process was not considered. This has rendered the theories incomplete and has been in pah the cause for errors in modelling the flow. In the first half of this study the Schwiebert and Leong model has been expanded to include the influence of viscosity change in the Underfill at the flow temperature. The resulting derivation is a more general form of the flow equation as compared to that of Schwiebert and Leong. The paper shows that the new equation can be reduced to the Schwiebert and Leong equation when the Underfill viscosity is considered to be constant. Experimental verification was done by first characterizing the viscosity change over time of three different Underfills. The flow distances versus time; the change in the rheology over the flow temperatures and time; and the change in 6he contact angle of the Underfill to a laminate substrate and polyimide die are also measured over time and temperature. The effect of the change in the contact angle over time at the Underfill flow temperatures and other parameters that influence Underfill flow are discussed These experimental results were then used to compare with the assumptions made in the theoretical prediction of the Underfill flow. Finally, the experimental flow results are compared with the theoretical model that was developed.

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High performance underfills development - materials, processes, and reliability

Cited by 42 publications

References 7 publications

Development of the wafer level compressive-flow underfill process and its involved materials

Development of the wafer level compressive-flow underfill process and its involved materials

Study on the relationship between the surface composition of copper pads and no-flow underfill fluxing capability

Rheology of the underfill flow process in a flip chip package

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