Universal surface-mount semiconductor package
In the fabrication of semiconductor packages, a leadframe is formed by masking and etching a metal sheet from both sides, and a plastic block is formed over a plurality of dice attached to die pads in the leadframe. A laser beam is used to form individual plastic capsules for each package, and a second laser beam is used to singulate the packages by severing the metal conductors, tie bars and rails between the packages. A wide variety of different types of packages, from gull-wing footed packages to leadless packages, with either exposed or isolated die pads, may be fabricated merely by varying the patterns of the openings in the mask layers and the width of the plastic trenches created by the first laser beam.
1. A method of fabricating a semiconductor package by using a leadframe, the leadframe comprising a plurality of die pads, a first semiconductor die being mounted on a first die pad, a second semiconductor die being mounted on a second die pad, the method comprising:
forming a plastic block, the plastic block covering said first and second semiconductor dice; and
directing a first laser beam against the plastic block and moving said first laser beam through a series of parallel adjacent scans, each of said series of scans removing a slice of said plastic block, so as to form a first plastic capsule and a second plastic capsule, said first plastic capsule covering said first semiconductor die, said second plastic capsule covering said second semiconductor die.
2. The method of claim 1 wherein each of said series of scans overlaps an adjacent scan of said series of scans.
3. The method of claim 2 wherein said leadframe further comprises a metal conductor, said metal conductor extending between said first and second plastic capsules.
4. The method of claim 3 wherein said first laser beam is of a first wavelength such that said first laser beam is absorbed less by said metal conductor than by said plastic block.
5. The method of claim 4 further comprising directing a second laser beam against said metal conductor so as to remove a portion of said metal conductor and thereby form a first lead and a second lead separated by a street, said first lead extending into said first plastic capsule, said second lead extending into said second plastic capsule.
6. The method of claim 5 wherein said directing a second laser beam against said metal conductor comprises moving said second laser beam through a series of parallel adjacent scans.
7. The method of claim 5 wherein said second laser beam is of a second wavelength such that said second laser beam is more readily absorbed by said metal conductor than said first laser beam.
8. The method of claim 5 wherein said first lead comprises a foot segment, a column segment and a cantilever segment.
9. The method of claim 8 wherein said directing a first laser beam against the plastic block is performed such that a side edge of first plastic capsule is positioned above one of said column segment and said cantilever segment of said first lead, thereby leaving a sidewall of said column segment of said first lead exposed.
10. The method of claim 8 wherein said directing a first laser beam against the plastic block is performed such that a side edge of said first plastic capsule is positioned above said foot segment of said first lead, thereby leaving both sidewalls of said column covered by said first plastic capsule.
11. The method of claim 8 wherein said directing a second laser beam against said metal conductor is performed such that a side of said street is aligned vertically with a side edge of said first plastic capsule so as to form a leadless semiconductor package.
12. The method of claim 5 wherein said directing a second laser beam against said metal conductor is performed such that a side of said street is aligned vertically with a side edge of said first plastic capsule so as to form a leadless semiconductor package.
13. The method of claim 5 wherein, following said directing a second laser beam against said metal conductor, a tie bar remains extending from said first plastic capsule, said method further comprising directing a third laser beam against said tie bar so as to cut off said tie bar flush with a sidewall of said first plastic capsule.
14. The method of claim 13 wherein said directing a third laser beam against said tie bar comprises moving said third laser beam through a series of parallel adjacent scans.
15. A method of fabricating a semiconductor package by using a leadframe, the leadframe comprising a plurality of die pads, a first semiconductor die being mounted on a first die pad, a second semiconductor die being mounted on a second die pad, the method comprising:
forming the leadframe from a metal sheet, said method of forming the leadframe comprising partially etching a backside of said metal sheet in a first location so as to form a cantilever segment of a lead;
forming, a plastic block, the plastic block covering said first and second semiconductor dice; and
directing a first laser beam against the plastic block so as to remove a portion of said plastic block and thereby form a first plastic capsule and a second plastic capsule, said first plastic capsule covering said first semiconductor die, said second plastic capsule covering said second semiconductor die.
16. The method of claim 15 wherein said method of forming a leadframe comprises partially etching a front side of said metal sheet in a second location horizontally spaced apart from said first location so as to form a foot segment of said lead, said first and second locations being separated by a third location wherein said metal sheet is not etched so as to form a column segment of said lead.
17. The method of claim 16 wherein said method of forming a leadframe comprises completely etching said metal sheet in a fourth location so as to separate said lead from a die pad.
18. The method of claim 17 wherein said method of forming a leadframe comprises etching said die pad from said backside of said metal sheet so are to form an isolated die pad.
19. The method of claim 15 wherein said method of forming a leadframe comprises completely etching said metal sheet in a fourth location so as to separate said lead from a die pad.
20. The method of claim 15 further comprising printing a layer of solder on a backside of said first die pad.
21. The method of claim 8 wherein said directing a second laser beam against said metal conductor comprises moving said second laser beam through a series of parallel adjacent scans, the energy of said scans of said second laser beam being varied so as to produce a rounded foot.
22. The method of claim 5 wherein said first lead comprises only a cantilever segment, said lead projecting horizontally from a sidewall of said first capsule.