WIKSTROEM BO (SE)
| EP0305696A2 | 1989-03-08 |
ELEKTRONIKTIDNINGEN, Nr. 16, 14-10-93, p. 19-20, (Sweden), PER HENRICSSON, "Snart aer Problemen Med Limmade Lomponenter Loesta".
IBM TECHNICAL DISCLOSURE BULLETIN, Vol. 31, No. 1, June 1988, "Extractor for Glued Small Surface-Mounted Components", pages 258-259.
ELTEKNIK MED AKTUELL ELEKTRONIK, Nr. 4, (25-02-88), p. 25 and 27 (SWEDEN), KERSTIN LJUNGGREN, "Limma Istaellet foer att loeda".
| 1. | A method for removing a surface mounted component from a circuit board, the component being attached by means of an adhesive joint, c h a r a c t e r i z e d in that the component and the adhesive joint are subjected to a thermal shock by being cooled down and in that the adhesive joint is imparted with internal mechanical stresses by the thermal shock, so that the component is loosened. |
| 2. | A method according to claim 1, c h a r a c t e r i z e d in that the component is exposed to a predetermined amount of a cooling medium for bringing about the thermal shock. |
| 3. | A method according to claim 2, c h a r a c t e r¬ i z e d in that the component is exposed to a predetermined amount of liquid gas. |
| 4. | A method according to claim 3, c h a r a c t e r¬ i z e d in that the component is exposed to a predetermined amount of liquid nitrogen gas. |
| 5. | A method according to any of claims 2 4, c h a r a c t e r i z e d in that the component is shielded in relation to other components, before it is exposed to the material for bringing about the thermal shock. |
| 6. | A device for removing a surface mounted component (11) from a circuit board (10) , the component being attached by means of an adhesive joint, c h a r a c t e r¬ i z e d by means (16, 17, 18) for supplying cooling medium to the component (11) and by control means (19) for con¬ trolling the supply of cooling medium. |
| 7. | A device according to claim 6, c h a r a c t e r¬ i z e d by shielding means (15) for shielding the component (11) from other components (12) and in that the control means (19) is intended for positioning of the shielding means (15) in relation to the component (11) . |
Technical Field
In the electronic industry it has recently become common to surface mount circuit components on circuit boards.
Components which have been surface mounted on circuit boards and which have been found to be defective have to be removed from the circuit board and be replaced by func¬ tioning components.
The present invention relates to a method and a de¬ vice for removing a surface mounted component from a cir- cuit board.
Technical Background
When the attachment between the component and the circuit board is performed in the conventional way by means of soldering, the removal is performed in a conventional way in that the solder joint is melted, so that the compo¬ nent is loosened.
It has become increasingly common to surface mount by means of electrically conducting or non-conducting adhes- ives, which often are epoxy based, so that the component is attached to the circuit board by means of an adhesive joint. As the most commonly used adhesives have different properties than solder material in relevant respects, the removal thus has to be performed in another way. The adhe¬ sive joint can normally not be loosened in a way which corresponds to melting of the solder joint.
Methods are given according to which the component is sheared loose by physical influence or is worked by means of impulse hammers or similar tools. It is also possible to use a rotationally oscillating tool for weakening the adhe- sive joint, so that the component is loosened. These methods are usually supplemented by local heating of the
circuit board for impairing the mechanical properties of the adhesive.
The techniques described above for removing compo¬ nents from circuit boards have several deficiencies. There is for example a great risk that the circuit board is made dirty and/or is damaged. It is also a clear risk that neighbouring components are damaged at such physical wor¬ king.
Short Summary of the Invention An object of the present invention is accordingly to bring about a method and a device for removing surface mounted components, the above described risks and drawbacks being avoided. The removal shall further be performed quickly and inexpensively. Different types of passive com- ponents as well as semiconductor components and non-en¬ closed chips are defined as surface mounted components.
This object is obtained in that the component and the adhesive joint are subjected to a thermal shock by being cooled down and in that the adhesive joint is imparted with internal mechanical stresses by the thermal shock, so that the component is loosened.
The Drawing
The invention will now be described by means of em¬ bodiments under reference to the attached drawing being a schematic perspective view of a device for carrying out the method according to the invention.
Detailed Description
The drawing shows a circuit board 10, on which a first component 11 and a second component 12 have been sur- face mounted by means of an adhesive joint on the circuit board. The circuit board is made of plastic and is provided with circuitry 13 and connection pads 14 of metal. The de¬ vice shown in the drawing comprises a tube 15, which is vertically movable in relation to the circuit board 10. The dimensions of the tube 15 are such that areas with other
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form and dimensions of the circuit board and the components the tube 15, the nozzle 17 and other elements of the inven¬ tion may be carried out in many different ways within the limits of the invention. Instead of by means of a tube 15, the shield can be brought about by means of a heat buffer or the like, for example by means of guided air streams. Other types of heat conduction may also solve the problem with the shielding or the isolation of the component which shall be removed. The method according to the invention is especially suitable at the removal of non-enclosed semiconductor com¬ ponents, chips and the like but is also suitable for other surface mounted components. For obtaining the best possible effect the thermal expansivity of the circuit board, the adhesive and the component shall be different, so that shear forces appear between them. The material in the cir¬ cuit board can be plastic, but also ceramic and other mate¬ rials may be used.
Most presently used adhesives, which are used in this application, get impaired strength at cooling down and the adhesive joint becomes brittle, which leads to the positive effect that a thermal shock by means of for example liquid gas gives a double effect and an especially good result.