Manufacturing solder-preform holders for a pick-and-place machine

• US 5,613,632 A
• Filed: 05/24/1995
• Issued: 03/25/1997
• Est. Priority Date: 12/04/1992
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Kohn, Harold
• Primary Examiner(s): Heinrich, Samuel M.
• Application Number:
  US08/449,320
• Time in Patent Office: 671 Days
• Field of Search: 228/246, 228/180.21, 228/207, 228/41, 228/49.5
• US Class Current: 228/246
• CPC Class Codes: B23K 2101/42 Printed circuits
• CPC Class Codes: B23K 3/08 Auxiliary devices therefor cleaning pipes or tubes or systems of pipes or tubes, e.g. before soldering, B08B9/02
• CPC Class Codes: H05K 3/3478 Applying solder preforms; Transferring prefabricated solder patterns
• CPC Class Codes: Y10S 206/821 Stacking member

Abstract

Rectangular preforms are vacuum picked and placed in each cavity of a first holder, and a measured amount of no-clean flux liquid is dispensed onto each preform, then a second holder is placed in an inverted position on top of the first holder and the holders are flipped so that the dry side of the preform is exposed and then a measured amount of no-clean solder is dispensed on the dry side of the preform. A robot arm with a rubber tipped vacuum probe picks up the preforms without damage or contamination and places them on a circuit board, grippers of the robot arm pick up and position a component on an induction coil to heat it up sufficient for reflow soldering, and then move the component onto the preform on the circuit board for reflow soldering. The circuit board can be used without cleaning with solvents or CFC'"'"'s, thus reducing process steps and reducing environmental hazards.

Claims

1. Method of assembling circuit boards, comprising the steps:

providing multiple holders for planar bodies with inwardly tapered cavities;

inserting bodies in about horizontal positions in the cavities so that edges of the bodies are supported by tapered sides of the cavities;

introducing a no-clean flux liquid into the cavities;

drying the bodies to provide a delicate coating of no-clean flux on at least one major surface of the respective bodies;

stacking the holders;

transporting the stack of holders;

providing a circuit-board substrate;

vacuum picking the bodies up from one of the holders and placing the bodies on component sites on circuit board substrates;

heating the circuit boards, and bodies sufficient for reflow soldered connection of the bodies to the circuit boards; and

cooling the circuit boards.

2. The method of claim 1 in which the bodies are solder-preforms.

3. The method of claim 1 further comprising the step of:

utilizing the circuit boards without cleaning to remove a residue of the flux.

4. The method of claim 1 in which the bodies include solder and further comprising the step of:

placing other components over the bodies on the component sites;

and in which during the step of heating, the solder is melted and the other components are heated sufficiently for reflow attachment of the other components to the circuit-board substrate.

5. The method of claim 1 in which the step of providing multiple holders incudes the step of:

providing holes through bottom walls of the cavities sufficiently large for draining any excess flux liquid from the cavity and to admit circulating air for drying the bottoms of the bodies.

6. The method of claim 1 in which the bottoms of the cavities are clear;

and further comprising the step of visually inspecting the bottoms of the bodies after the flux liquid has been dried.

7. The method of claim 1 in which the holder is planar and an angle between sidewalls of the cavities and a planar surface of the holder into which the cavities are formed is between about 15 and about 60 degrees and provides for self centering of the bodies when the bodies are slightly vibrated with respect to the holder.

8. The method of claim 1 further comprising the step:

providing a hole in one corner of the holder and a slot at another corner of the holder with a width of the slot substantially different from a diameter of the hole.

9. The method of claim 1 further comprising the step:

providing multiple holder sites with two different sized posts extending up from each holder site; and

unstacking the holders and positioning them onto respective holder sites with the two posts extending through a respective hole and slot.

10. The method of claim 1 in which the bodies are planar solder preforms, and further comprising the step of:

placing another component with about the same planar dimensions as the preform, over the preform on the circuit board substrate; and

reflowing the component to connect the other component to the circuit-board substrate.

11. The method of claim 1 further comprising the steps of:

after the step of drying, placing a second holder inverted over the first holder;

turning both holders over to invert the bodies and transfer them to the second holder;

introducing no-clean flux liquid onto the tops of the inverted bodies; and

drying the bodies to provide a coating of no-clean flux on both sides of the bodies.

12. The method of claim 1 in which the step of drying the bodies includes moving the holders through an oven at a temperature significantly above ambient conditions.

13. The method of claim 1 in which the holders include spacers attached to a bottom surface, which spacers are sufficiently thick so that when the holders are stacked the spacers support bottom walls of respective upper trays, above bodies in cavities of respective lower trays to protect the coating of flux, and are sufficiently thin to prevent the bodies from exiting the stack when the stack is accelerated or tipped during the transporting step.

14. The method of claim 2 in which the rectangular sheet is square.

15. The method of claim 1 further comprising:

providing multiple holders includes;

heating a rectangular sheet of clear polycarbonate above the transition temperature.

16. The method of claim 1 in which providing multiple holders includes vacuum molding an array of continuous rectangular frustropyramidal section cavities with sidewalls of cavities extending at least about 2 mm from one side of the sheet to about flat bottoms about parallel to the sheet with the walls of the cavities tapered inward toward the center of the cavity at an angle of about 30-60 degrees for supporting each edge of a thin, planer, rectangular, body with major dimensions at least about 2 mm larger than the major dimensions of the cavity bottom wall to support the preform suspended at least about 1 mm above the bottom of the cavity to prevent trapping liquid between the preform and the bottom of the cavity and allow circulation of drying air to the bottom of the preform.

17. The method of claim 1 in which providing multiple holders includes connecting spacers at least about 1 mm high to the bottom surface of the holder for positioning vertically stacked holders so that the bottoms of the cavities of each upper holder extends into the cavities of each lower holder leaving a gap above the bodies so the body is held in place without damaging the layer of flux on the body.

18. The method of claim 17 in which providing multiple holders includes forming a hole through the sheet and connected spacer at one corner of the sheet and forming a slot with round ends through the sheet and connected spacer at the diagonally opposite corner of the sheet with a width substantially different than the diameter of the hole.

19. The method of claim 1 in which stacking the holders includes,

inserting the hole and slot of each holder onto two respective posts extending upward from a bottom frame which is more rigid than the holders.

20. The method of claim 1 in which stacking the holders includes,

inserting an empty holder over the stack to provide an upper holder for the top holder which contain bodies.

21. The method of claim 19 in which stacking the holder includes;

inserting a top frame and dust cover over the posts; and

threading nuts over the posts to compress the holders between the top and bottom frames.

22. The method of claim 1 in which the flux coating on the bodies is inspected by looking through the bottom of the holder prior to stacking.

23. The method of claim 1 in which the holders are unstacked and loaded in an automatic pick-and-place machine with different sized posts at each holder position of the machine extending upward through the corner hole in one corner and through the slot of the diagonally opposite corner to fit snugly on the posts.

24. The method of claim 1 in which the bodies are automatically removed from the holder using an elastomer surfaced vacuum pickup to prevent damage to the delicate flux coating.

25. The method of claim 1 in which the body is automatically placed on a circuit board substrate at sites for another component.

26. The method of claim 1 in which the body is place on a circuit board and an other component is placed over the body.

27. The method of claim 26 in which the circuit-board substrate, body and other component are heated in an over for reflowing to form a reliable solder joint between the other component and the circuit-board substrate.

28. Method of manufacturing circuit boards, comprising the steps:

providing multiple body holders with inwardly tapered cavities with holes at the bottom of the cavities to drain liquid from the cavity and allow air to circulate through the bottom of the cavity;

inserting planar bodies in about horizontal positions in the cavities so that edges of the bodies are supported by the tapered sides of the cavities;

introducing a no-clean flux liquid into the cavities onto the bodies;

drying the bodies to provide a delicate coating of no-clean flux on at least one major surface of the bodies;

stacking the holders;

transporting the stack of holders;

providing a circuit board substrate with component sites;

vacuum picking bodies up from one of the holders and placing the bodies on a circuit board at the component sites;

placing components over the bodies at the component sites;

heating the circuit boards, bodies and components sufficient for reflow soldered connection of the components to the circuit boards; and

cooling the circuit boards.