Method and apparatus for welding printed circuits

Abstract

An induction head for bonding stacked layers ( 19, 20 ) for making printed circuits, by electromagnetic induction. A magnetic flux is locally induced at a plurality of conducting spacers ( 25 ) provided along a peripheral area ( 22 ) of the multilayer stack ( 18 ). With this induction head, it is possible to induce magnetic fluxes with opposite sign in individual areas of the peripheral are, thus achieving the maximum energy efficiency during the bonding process.

1 . An induction bonding head ( 3 ;  30 ) for carrying out bonding of a printed circuit multilayer stack ( 18 ), wherein the stack comprises a plurality of conducting layers ( 19 ) incorporating the printed circuit layout ( 21 ), the conducting layers respectively being separated from each other by a plurality of insulating layers ( 20 ) made of dielectric material impregnated with resin, a plurality of spacers ( 25 ) being arranged continually along the edges of the conducting layers ( 19 ) in order to keep the conducting layers spaced apart along the edges, the bond head comprising:
 a first induction core ( 12 ;  120 ) associated to an excitation inductor ( 3 ); and   a second induction core ( 4 ;  120 ′) cooperating with the first induction core to bring a magnetic flux to a bonding area between the first and the second induction cores, wherein at least one of said first and second induction cores ( 12 ,  120 ;  4 ,  120 ′) has two magnetic poles with opposite magnetic polarity, oriented towards the bonding area ( 5 ) of the multilayer stack ( 18 ), whereby a same magnetic flux passes therethrough.   
     
     
         2 . The induction bonding head ( 3 ;  30 ) according to  claim 1 , wherein the first induction core ( 12 ;  120 ) comprises a body made of magnetically permeable material with a substantially “C” shape, wherein a pair of end arms ( 12   a,    12   b;    120   a;    120   b ) are connected to a central arm ( 12   c;    120   c ), an inductor ( 13 ,  130 ) being associated thereto for inducing the magnetic flux in the two end arms ( 2   a,    2   b ). 
     
     
         3 . The induction bonding head ( 3 ;  30 ) according to  claim 1 , wherein the second induction core ( 4 ) comprises a substantially plate-like element made of ferromagnetic material. 
     
     
         4 . The induction bonding head ( 3 ;  30 ) according to  claim 1 , wherein the second induction core ( 4 ,  120 ′) comprises a body of a magnetically permeable material having a substantially C-shape, wherein a pair of end arms ( 12   a,    12   b;    120   a;    120   b ) are connected to a central arm ( 12   c;    120   c ), an inductor ( 13 ;  130 ) being associated thereto for inducing the magnetic flux in the two end arms ( 2   a,    2   b ). 
     
     
         5 . The induction bonding head ( 1 ,  12 ) according to  claim 1 , further comprising a thermal barrier ( 17 ,  170 ) applied on at least an end portion of said parallel arms of the C-shaped core. 
     
     
         6 . An induction bonding apparatus ( 1 ) for printed circuit multilayer stacks ( 18 ), comprising a plurality of induction bonding heads ( 3 ;  30 ) according to  claim 1 . 
     
     
         7 . The apparatus according to  claim 6 , wherein the bonding heads ( 3 ,  30 ) translate along guides ( 4 ) arranged at opposite sides. 
     
     
         8 . The apparatus according to  claim 7 , wherein the cores ( 12 ,  4 ;  120 ,  120 ′) of the bonding heads ( 83 ,  30 ) are supported in such a way that they can be rotated with respect to a substantially vertical axis, to be oriented in a direction parallel or perpendicular to the edge of the multilayer stacks to be welded.