Coating processes – Electrical product produced – Integrated circuit – printed circuit – or circuit board
Reexamination Certificate
1998-01-12
2001-07-03
Talbot, Brian K. (Department: 1762)
Coating processes
Electrical product produced
Integrated circuit, printed circuit, or circuit board
C427S312000, C427S294000, C427S313000, C029S840000, C029S830000, C228S180220, C228S253000
Reexamination Certificate
active
06254923
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to attachment of integrated circuits to substrates in electronic equipment and more particularly to attachment of direct chip attach (DCA) integrated circuits (or chips) to printed circuit boards using solid solder particles.
BACKGROUND OF THE INVENTION
Presently, DCA chips are bonded to metallized contacts (DCA sites) arranged on substrates such as printed circuit boards (PCB's) by applying molten solder particles to a substrate, flattening the particles, applying sticky flux to the substrate, placing components (DCA chips) onto the flattened particles and reflowing the joints.
IBM Research Disclosure 27109 describes a tool for placing solid solder balls on a ceramic surface solder device. The balls are of the order of 0.625 mm diameter. The ceramic surface mount device is screen printed with sticky solder paste only at contact sites and the device positioned above a template having an arrangement of apertures containing balls positioned to correspond to the sticky solder paste sites. The balls are held in place on the template by gravity with assistance from a vacuum, which is released to allow the sticky solder paste on the surface mount device to extract the balls from the template. The use of a template with a vacuum also aids the installation of the balls onto the template as the balls are simply spilled over and fall into place on the template.
DCA sites have contacts at a very fine pitch, so it is critical that an exact volume of solder is deposited onto the DCA sites to form a joint. Too little solder will result in an open circuit, while too much solder will result in a short circuit. Another problem is that solder pastes cannot be readily printed to such a fine pitch, as clogging of the apertures used for printing results. In addition, paste registration to DCA sites over a whole substrate would be impossible.
A repair of an open circuit or a short circuit contact for this technology is difficult so a method that can guarantee accurate deposition volume to minimize repair activity is desired. Deposition of molten solder requires an inner and outer mask to be accurately aligned to each other, and then the combination aligned to the DCA site. The alignment of the inner and outer masks is both difficult and time consuming with no guarantee that the finished mask will give the required volumes on all DCA sites. Other variable parameters which must be precisely controlled include the thickness of inner and outer masks used to deposit the molten solder, hole size of the inner mask, stand off height of the outer mask and the air pressure which forces molten solder through the masks.
SUMMARY OF THE INVENTION
The invention provides a method of depositing solder from a reservoir onto metallized contacts arranged on a surface via a pick-up head comprising applying flux to the contacts, picking up solder in the form of particles from the reservoir with the pick-up head, the head having apertures corresponding to the arrangement of the contacts, positioning the head adjacent the contacts, aligning the apertures with the contacts, and releasing the particles onto the surface, the particles being retained on the surface by the flux.
Preferably, the method further comprises, after releasing the particles, reflowing the solder particles, leveling the reflowed particles with a flattened head to form reliefs, applying flux to the reliefs, placing integrated circuit contacts onto the reliefs, and reflowing the reliefs to attach the chip to the surface. The pick-up head preferably picks up and releases the solder particles by applying and releasing a vacuum. The solder particles are preferably maintained in a fluidized form while being held in the reservoir. This prevents the solder particles sticking together.
In a preferred embodiment of the present invention, there is provided an apparatus for denting solder from a reservoir onto metallized contacts on a surface comprising means for supplying a surface, the surface having a plurality of contacts arranged thereon, to the apparatus, a reservoir for containing solder particles, the particle size corresponding to the size of the contacts, means for producing a vacuum, a pick-up head having a connection for the vacuum producing means and a plurality of apertures smaller in size than the solder particles and having an aperture configuration corresponding to the arrangement of the plurality of contacts, the head being capable of being positioned in a first position adjacent the reservoir and a second position adjacent the surface, means for dispensing flux onto the contacts, control means for causing the head to transport the particles from the reservoir to the surface, means for aligning the apertures with the contacts and means for controlling the vacuum to the pick up head.
Preferably, the apparatus further comprises a rotating turret with the heads positioned circumferentially. The turret has an indexing system and is computer controlled.
REFERENCES:
patent: 5093986 (1992-03-01), Mandai et al.
patent: 5118027 (1992-06-01), Braun et al.
patent: 5203075 (1993-04-01), Angulas et al.
patent: 5205896 (1993-04-01), Brown et al.
patent: 5255839 (1993-10-01), Da Costa Alves et al.
patent: 5409157 (1995-04-01), Nagesh et al.
Boyd Alexander
French William
Lees Stuart P.
Murray Kenneth Skene
Robertson Brian L.
Clarkson Douglas M.
International Business Machines - Corporation
Talbot Brian K.
LandOfFree
Solder particle deposition does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Solder particle deposition, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Solder particle deposition will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2536449