Solder Flip Chip

First, the chip is picked up from a waffle pack with a vacuum tool. The chips are presented for pick-up with the solder bumps facing down. The chip is then dipped into flux to coat the solder bumps. It is important that the flux only covers the bumps and not the entire bottom of the chip so that the tool can easily remove the chip from the flux without sticking.

Next, the chip’s solder bumps are aligned to the substrate bond pads. The chip is then placed on the substrate at a controlled bond load for a specific amount of bond time. Bond loads and times may need to be adjusted.

In the final step of the process the chip is sent to reflow. The most common method is to transfer the substrate with the placed chip to a reflow oven, which runs a thermal profile. In an alternate method, the chip is heated by a heating system that can run a thermal profile to reflow the solder. This method is useful in placing a flip chip onto a populated circuit and for rework.

A holder that presents the chip for pick-up is required.  The holder should be able to accommodate a waffle pack tray, which is the most common container for flip chips.  The machine needs a vacuum pick-up tool that can pick-up the die, dip it into the flux, and place it on a substrate.  The pick-up tool should be driven by a system that can apply various bond loads.

A flux tray is required to apply flux to the die.  The flux can be applied manually, by brushing the flux over the bond site or the chip can be dipped into a layer of flux in a fluxing tray.  The layer of flux is evened out with a doctor blade, which can be either a manual or motorized unit.

A workstage is requires to hold the substrate steady and keep it co-planer to the chip.  If the chip is going to be reflowed, the stage needs to be heated.  The stage also needs to support the substrate for alignment to the chip.  For the alignment process, a system that shows the substrate pads and solder bumps is required.

The chip needs to be placed by a system that can deliver enough bond load to sufficiently seat the chip.  Flip chips with a greater quantity of bumps require a higher bond load.

If the reflow is done on the machine, a heated stage and a heating system that can run thermal profiles are required.

The standard Model 850 includes a die tray pedestal that presents chips in waffle packs for pick-up tool.  Various sized pick-up tools are available.  Motorized or manual fluxing stations are available for the fluxing process.  The motorized station has a rotating flux pot with a micrometer adjusted doctor blade.  The flux pot can be heated to reduce viscosity of the flux.  This flux station can also be used to apply conductive adhesive.   The manual flux station is equipped with a hand-held flux doctor blade.

This machine is equipped with a cube beam splitter vision system, which shows superimposed images of the chip solder bumps and substrate pads  on a color monitor for alignment,  A color camera with a zoom lens transmits the image.  The standard magnification range of the zoom is 15X – 100X.  Higher ranges are available.

A micrometer-adjusted stage with a 4 X vacuum chuck supports the substrate for chip alignment and placement.

For reflow on the system, a temperature controlled, 4 X 4 heated stage capable of 350°C. is available as is a hot gas spot heating system, which mounts on the Model 850.  This system has interchangeable nozzles and uses low gas velocity to localize the heating.

• Model 850 Semi-Automatic Flip Chip Placement System
• Die Tray Pedestal
• Manual Fluxing Station or Motorized Fluxing Station

• Model 855 Heated 4 X 4 Workstage
• Model 430 Hot Gas Rework Module