|A publication of the National Electronics Manufacturing Center of Excellence||December 2004|
Michael D. Frederickson
Chip on Board is a hybrid technology that employs bare die devices interconnected to printed circuit boards (PCBs). The connections can be made by wire bonding, tape automated bonding (TAB), or flip chip bonding.
The following are Tech Tips to improve Chip on Board assembly:
1. Before attaching the bare die to PCB, burnish the wire bond pads with a soft wire brush. Cleaning will help to eliminate oxidation build up (Figure 5-1).
2. Use a vacuum tool tip to die attach the bare die, as it is critical to protect the bare die from mishandling. Use of a vision system will help eliminate inconsistent die misplacement. Conductive or non-conductive epoxy can be used for attachment compounds. After die attachment, use plasma cleaner to reduce epoxy bleed-out (O2 plasma cleaning might discolor conductive epoxy). It is recommended to use Argon gas to reduce discoloration in plasma cleaning. Figure 5-2 shows “Target” bare die attachment.
4. Make sure the unit is properly clamped in the work holder. It is critical that no movement takes place. Verify there is no movement by nudging the object with tweezers. If movement takes place, the unit must be secured during high speed bonding.
5. Make sure the wedge tool is in functional condition. Factors such as bond size, bond pad pitch, wire diameter, harness type, and metallization have an effect on bonding performance. The proper tool selection is essential for consistent wire bonding.
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