Fine pitch solder formation on printed circuit board process and product

• US 5,493,075 A
• Filed: 09/30/1994
• Issued: 02/20/1996
• Est. Priority Date: 09/30/1994
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Partridge, Julian P., Sanghavi, Bhavyen S., Chong, Ku H., Crockett, Charles H. Jr.
• Primary Examiner(s): TSO, LAURA K
• Application Number:
  US08/315,746
• Time in Patent Office: 508 Days
• Field of Search: 174/250, 174/259, 174/260, 174/261, 228/179.1, 228/180.21, 228/180.22, 361/760, 361/765, 361/767
• US Class Current: 174/261
• CPC Class Codes: H01L 2224/16225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H05K 2201/09727 Varying width along a single conductor; Conductors or pads having different widths
• CPC Class Codes: H05K 2201/10674 Flip chip
• CPC Class Codes: H05K 2203/044 Solder dip coating, i.e. coating printed conductors, e.g. pads by dipping in molten solder or by wave soldering
• CPC Class Codes: H05K 2203/0485 Tacky flux, e.g. for adhering components during mounting
• CPC Class Codes: H05K 2203/0574 Stacked resist layers used for different processes
• CPC Class Codes: H05K 2203/0769 Dissolving insulating materials, e.g. coatings, not used for developing resist after exposure
• CPC Class Codes: H05K 2203/1476 Same or similar kind of process performed in phases, e.g. coarse patterning followed by fine patterning
• CPC Class Codes: H05K 3/1216 by screen printing or stencil printing
• CPC Class Codes: H05K 3/341 Surface mounted components
• CPC Class Codes: H05K 3/3452 Solder masks
• CPC Class Codes: H05K 3/3468 Applying molten solder
• CPC Class Codes: H05K 3/3485 Applying solder paste, slurry or powder thick film methods for applying conductive paste or ink patterns H05K3/12

Abstract

A method, and product created thereby, by which low melting point solder suitable for reflow connection of components is formed on select fine pitch contacts of a printed circuit board. The method is particularly suited to the attachment of flip-chip die to printed circuit boards which also include coarse pitch surface mount components. Controlled volumes of solder are formed onto fine pitch contacts of the printed circuit board through selective holes in a mask formed onto the board. The deposit is accomplished by molten solder immersion preferably using conventional hot air solder level manufacturing equipment. The volume of solder is related to the thickness of the mask. The mask is then removed, the deposited low temperature solder is flattened, and the coarse pitch contacts are covered with solder paste in a conventional screening process. Flux is applied to the fine pitch contacts. After component placement, the solder reflow connects in one operation both the fine and coarse pitch components to their respective printed circuit board contacts.

Claims

1. A printed circuit board, comprising:

a dielectric structure core;

a conductive interconnect layer with fine and course pitch contacts on at least one surface of the dielectric structure core;

solder of first volume formed on select conductive layer fine pitch contacts by;

forming a mask over the surface having the conductive interconnected layer;

depositing solder of first volume consistent with the mask through openings in the mask by molten solder immersion; and

stripping the mask to expose both fine and coarse pitch contacts; and

solder paste formed in a second volume, materially greater than the first volume, on select conductive layer coarse pitch contacts.

2. The product recited in claim 1 wherein the solder formed on the fine pitch contacts is comprised of flattened solder balls.

3. The product recited in claim 2, wherein the solder paste is stencil deposited.

4. The product recited in claim 3, wherein the fine pitch contacts are at a pitch materially less than 16 mils while the course pitch contacts are at a pitch nominally 16 mils and greater.