Release Film Boosts IC Molding Productivity
Kenji Tsuda, Asia Contributing Editor -- Semiconductor International, 7/23/2008 7:48:00 AM
A new molding technology that uses a heat-endurance film is on the horizon that may boost IC packaging productivity by making it easier to remove molded chips from the mold, according to Asahi Glass Co. Ltd. (Tokyo).
The film was developed after customers said they wanted more effective resin usage. Without the release film, conventional molding technologies require cleaning the rear surface of ball grid arrays (BGAs) or chip-scale packages (CSPs). Cleaning the molding machine itself every day, as well as designing ejector pins for individual metal molds, are “troublesome steps” that can be eliminated by the plastic release film, said Yuki Sakamoto, a marketing manager at the Multi-Functional Film Business Group of the AGC Chemicals Fluoro Products Division of Asahi Glass.
Thinner BGAs or CSPs, with a thickness of only 0.4 mm, require an easy-to-flow resin. Conventional transfer molding must push molten resin from a gate and runner to distant chips on a board. Also, the resin tends to flow into the backside of the BGA or CSP board. The backside surface must be mounted with solder balls, but if there are residues from the resin, solder balls tend to detach. The release film plays the role of a cushion to the upper and lower metal molds. The resin does not attach to the upper metal mold directly due to the film, leading to fewer cleanings.
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| A molding tape film reduces the need for cleaning, and supports mold designs without ejector pins. |
Conventional molding technology requires cleaning every day; typically one cleaning after 150-200 shots. If the metal mold is not cleaned, the adjacent molded package may become dirty. With the release film, cleaning is required only once every several months.
According to Asahi Glass, the plastic film conforms to the mold surface without corrugation. The conformal film removes the need for ejector pins for release from the metal mold, leading to higher design freedom of the substrate board. In the conventional approach, ejector pins are needed at the border between chips in order to not damage the ICs.
The release film has a heat endurance of >180°C with little shrinkage. Asahi Glass also sells the Aflex series film for protecting solar cells, and it is being used to protect the Beijing Olympic stadium’s domed roof.
