BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of an amorphous carbon coated polyimide film layer used in an IMS head.
FIG. 2A is a side view of an IMS head with amorphous carbon coated polyimide film used as the solder injection aperture assembly.
FIG. 2B is a bottom view of an IMS head with amorphous carbon coated polyimide film used as the solder injection aperture assembly.
FIG. 3 is a schematic of an IMS head with amorphous carbon coated polyimide laminated on a thin flexible metal sheet used as the solder injection aperture assembly.
FIG. 4A is a schematic of a bottom view of an O-ring sealed IMS head.
FIG. 4B is a schematic of a side view of an O-ring coated with amorphous carbon film.
DETAILED DESCRIPTION
FIG. 1 is a side view of a part of an IMS head according to an embodiment of the invention. A polyimide film layer (such as Kapton® polyimide film) 102 is coated with an amorphous carbon layer 104. The amorphous carbon layer 104 may be deposited by plasma sputter deposition, laser ablation, ion beam assisted deposition, direct ion beam deposition, ion beam sputter deposition, plasma enhanced CVD (chemical vapor deposition), or microwave ECR (Electron Cyclotron Resonance) CVD or other suitable processes. The thickness of the amorphous carbon layer 104 can be in the range of 50 to 2000 Angstroms. The optimal thickness of the amorphous carbon layer 104 is thick enough to provide the carbon characteristics of low friction, but not so thick as to cause cracking or delaminating due to thin film stress. The use of the above materials provides low friction sliding of the bottom surface of the head, while remaining stable at temperatures up to 400 degrees C., and providing compliance during the scanning of a surface which may have protrusions.
FIG. 2A is a side view of an IMS head 200 with a solder injection aperture 212. The IMS head 200 comprises a base plate 202, a solder reservoir 204, a polyimide film layer 206 (similar or identical to layer 102), and an amorphous carbon layer 208 (similar or identical to layer 104). The aperture 212 (shown in broken lines) leads to a slot 210 (also shown in broken lines) for holding solder to be dispensed on a circuit board surface. FIG. 2B is a bottom view of the IMS head 200. The part of the IMS head 200 with the aperture 212 is shown with the slot 210. The slot is formed through the polyimide film layer 206 and the amorphous carbon layer 208, exposing a part of the base plate 202 to the bottom of the head 200. This IMS head 200 is typically operated by the following method. The IMS head 200 sits on a mold with cavities which is to be filled with solder. The molten solder containing the IMS head 200 is scanned over the mold surface while pressure is applied to the solder reservoir. The solder is forced to flow through the small aperture 212 due to applied pressure from above and it fills the aperture area 210. The solder cannot escape from the aperture 210 until it encounters a cavity on the surface of the mold. As the aperture 210 of the IMS head 200 passes over the cavity in the mold, the solder is dispensed and fills the cavity. The friction during scanning is lowered by the low friction coating 208. In one embodiment, the amorphous carbon 208 is deposited by a RF (radio frequency) sputter deposition method. The polyimide film surface 206 is pre-treated by standard brush cleaning with a detergent followed by an oven bake at 140 degrees C. for two hours to bake out any water absorbed in the polyimide, then O2 plasma ash is applied to promote good adhesion. The Carbon deposition system is operated at 300 Watts for thirty minutes to degas the chamber. The RF power during deposition for the actual deposition is at 200 Watts. For this application, the system is operated for four hours to give an amorphous carbon thickness of about 500 Angstroms.
FIG. 3 is a schematic of an IMS head 300 similar to the one shown in FIG. 2, but with an additional feature of a thin flexible metal sheet 302 supporting the low friction thin film coated polyimide film sheet 206. The head 300 includes a set of springs 304 disposed between the base plate 202 and the thin flexible metal 304. The thin flexible metal sheet 304 provides additional compliance over a large area. The polyimide film layer 206 can be easily laminated onto the metal sheet. Details of a similar scheme is described in previous U.S. Pat. Nos. 6,056,191 and 6,527,158, which are hereby incorporated by reference.
FIG. 4A is a schematic of a bottom view of a fluoroelastomer O-ring 402 sealed IMS head 400. The solder is dispensed from an aperture 404 (in the IMS head bottom plate assembly 406) and is contained within the O-ring 402. As the IMS head 400 scans over the mold, solder is injected into ariy cavities it passes over. FIG. 4B shows the O-ring 402 with a thin layer of amorphous carbon 406. The coating performed on the side where the O-ring 402 makes contact with the mold. Only one side is being deposited as that side is the sliding surface. In principle, the low friction coating 408 can be applied to the surface opposite of the O-ring surface, in this case, the mold surface. The situation (e.g., economics, durability etc) will dictate whether the O-ring 402 or mold gets coated. However, it is possible both sides receive the coating for minimizing the friction and wear. While fluoroelastomer is used for the O-ring in this embodiment, any compliant material with thermal stability can be used.
Therefore, while there has been described what is presently considered to be preferred embodiments, it will be understood by those skilled in the art that other modifications can be made within the spirit of the invention.
Patent Application
20080014406
