An overview of new molding solutions using film in mold
Topics
Abstract
Film Technology for BGA and
uBGA packages
Conclusion
Abstract
Today's molding engineers face the challenge of encapsulating silicon devices of ever-increasing complexity in smaller and thinner package configurations while having to work with superior molding compounds to meet the most stringent, cost effective customer circuit and package performance requirements.
FAM technology is an enabling material and process technology that addresses these challenges. By carefully analyzing the features of FAM technology, it is possible to economically manufacture advanced packages in high volume production while achieving the highest device reliability.
Film in cavaties
Figure 1. Film for easy release
With the use of FAM, since the mold compound is not sticking to the mold, Ultra thin packages on substrate or on tape are easily released from the cavity and the packages are not damaged during the release process. The method provides inherently higher reliability (See fig. 1).
This article will:
Provide an introduction into FAM and will
Explore the possibilities and the benefits that FAM brings to semiconductor
...package encapsulation.
Provide the reader with ready to use solutions for.advanced packages
Film Technology for BGA and uBGAThe ETFE-film has a high tear resistance and can work at temperatures as high as 200C. After loading the lead frame or substrate into the mold, the transfer molding and curing occurs. The mold is then opened and the lead frame or substrate is unloaded. Before the next cycle is started, the vacuum is removed. The film is then transported one length of the mold to renew the film.This technology is typically used with ultra thin packages in MAP molded applications in Mini or Matrix BGA,Flip Chip in Package or Wafer Level Packaging.
Features of Release Film Technology:
No mold wear on the film side of the mold
No ejection on the package
Higher yield ultra thin BGA devices. In all processes where film is applied, the film is sucked down to the inner surface of the mold before the lead frames are loaded in the mold. After vacuum is activated on the outside surface of the mold, the inner vacuum is activated and the film exactly follows the outline of the mold. The film is capable to follow the three-dimensional form of the cavities.
Film protecting the die
Figure 2. Exposed die clamping
The encapsulation makes use of a ETFE modified thermoplastic film, which is sucked down in two steps onto the surface of the mold. This technology also lends itself to exposed die molding found in such applications as optical sensor, pressure sensors or fingerprint sensors. By clamping the film around the chip's functional area, the surface of the chip is protected from the compound and will be bleed and flash free. (See fig 2). If desired, this technique allows over molding a part of the chip.
Adhesive Film Technology for LLP's and
QFN
Adhesive Film Technology for LLP's and QFN packages presents
a better and low cost alternative to pre-taped lead frames. The patented
Boschman AFT process is a high volume, production ready, high quality,
and
low cost solution of in flow lamination and delamination( Figure 5).
The die-and wire bonded lead frames are loaded in the mold
on the film (step 1).
Film Technology allows the package designer to create a bleed and flash free encapsulation process. LLP's or QFN in matrix lead frames are molded with the film below the lead frame. The film seals the leads and die pads against mold compound bleed and flash. The film functions as a gasket between the chip area and the mold and protects the chip surface from bleed and flash. (See fig 3).
Step 1.
Figure 3. Film as seal
A product specific
lamination tool presses the lead frames at specified positions on the
hot seal layer of the film (step 2). Only four additional seconds are
needed for the lamination process.
Step 2.
After the lamination tool is retracted, the
mold closes and normal encapsulation occurs. (step 3) After mold compound
curing and
mold opening, the molded strips are still on
the film.
Step 3.
The film, together with the lead frame, is released from the
mold and the film together with the strips are transported out of the
mold. (step 4) During this transport operation, the lead frames are automatically
peeled off of the film.
Step 4.
Used with pre-plated lead frames or the SFT process. During lamination
the intrusion of the AFT film between the leads is less than 4 um and
compensated by the molding pressure during cure.
The COO of AFT
The advantages of the AFT process are not limited to the quality aspects
of no intrusion
and no bleed. The die and wire bonding
process is based on the existing standard
die and wire bonding processes. The AFT film
is automatically applied during the molding process and peeled-off during
unloading of
the mold. Boschman Flexstar/FAM
encapsulation equipment, is equipped for the AFT process. No separate
process steps are needed for lamination and de-lamination. Buffing or
polishing operations before tin
plating are obsolete.
The melting characteristics of this hot seal layer and the well defined layer thickness, guarantee good adhesion to the lead frame by building up resistance against compound flow below the leads and therefore preventing bleed on the leads. In working with worldwide-represented polymer film manufacturers and choosing one type of standard polymer as the carrier, a special hot-seal layer has been developed with:
Specified melt characteristics
A defined layer thickness for best adhesion and...sealing
Minimized and residue free peel-off ...properties from the
...lead frame and mold compound.
No silicon residue on the lead frame.Adhesive Film Technology was developed to protect large areas of Molded Array Packages and is a reliable and low cost solution for the lamination of tape onto lead frames. Typical applications include low pin count packages, ranging from 2 to 80 pins, such as a CSP, SOT-23 or any discrete product in LLP. (See fig. 4)
Figure 4. Bleed and flash free leads
With AFT there is no intrusion on the package bottom.
The intrusion of the film between the leads is negligible. In the pre-taped process the film is compressed under the leads and on all areas where sealing is needed. The compressed film below the leads moves in between the leads ands causes a film protrusion resulting in a package intrusion after encapsulation. The adhesive layer of the AFT film is very thin and the PET-polymer carrier has a higher E modulus than the ETFE or Polyimide type film typically.
The PET-type polymer film carrier with the hot-seal layer is an extremely low cost film and costs less than a sixth of those films used in the pre-taped technology. The AFT COO is the lowest of any competing technology. For lead frame dimensions 50 X 195 mm the film costs per frame are:
Pre-taped: US$ 0.53, AFT: US$ 0.08.Resulting in a total saving of more than US$ 250.00 per year on a one chase system.
ConclusionIf you have questions about Boschman, contact info@boschman.nl.
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