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     The Callenge of 01005 and 0.3mm Assembly (March 2007)

            
 Scope:
             
             
The emergence of the miniature passives 0201 and 01005 and the CSP products with pitch of 0.4 mm and 0.3mm
             enables minimizing PCB area while imposing a challenge to the PCB editor and assembler.
             Lead free assembly process contributed to the challenge since the experience gained with this technology is not mature.
             Some case studies were done lately on assembly issues of 01005 resistors and of BGA with 0.3mm pitch.
             The findings, some of them surprising, are summarized below.

             
Definitions:

              0201 resistor passive size is - 600µm × 300µm (24mils × 12mils)













              01005 resistor passive size is - 400 µm × 200 µm (16mils × 8mils)











              Area aspect ratio - the ratio between the width of the stencil aperture and the area of the aperture walls. it should be > 0.66
              Paste type 3 - a solder paste with ball diameter of 25-45µm
              Paste type 4 - a solder paste with ball diameter of 25-38µm

             
Findings:

              Resistor pad size for 01005 components can be - 7×7 mils square or 7.3 mils diameter round and 7 mils spacing. Larger pads
               result in more bridging and tombstoning defects
              Square pads show a little better results than round pads
              0.1mm distance between two resistors pads results in 3%-4% bridging defects. Increasing distance to 0.125 mm reduced
               defects to ˜ 0.5%
              Tombstone defect was about 0.5% in components with no via in pad. Defects ramped to about 2% with 2 vias (one in each
               pad) and to 2.6% with one via only
              Components orientation has very little effect on defect percentage
              Pad size for 0.3mm CSP is 0.13mm. Ball size is 0.195mm
              Electro Formed fabricated stencils are best. Laser stencils are good
              Stencil thickness of 3 mils and paste type 4 give the best results
              Stencil thickness of 3 mils and paste type 3 give reasonable but not sufficient results
              Stencil thickness of 4 mils and paste type 3 are 'suicide' for 01005 component
              Printer speed, print pressure, wipe method and separation speed have almost no effect on the results
              Paste height is almost the thickness of the 01005 component. Nozzle cleaning is frequently done
              Lead free paste shows more resistance to tombstoning
              Surprisingly, 01005 are more resistant to tombstoning than 0201

            
 Issues that still have to be checked:

              Pad size optimization - geometry and dimensions
              Multilevel (stepped) stencils

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