METHOD OF FORMING A LEADFRAME FOR A SEMICONDUCTOR PACKAGE
A method of forming a leadframe (10) provides blocking fulcrums (21,23) adjacent to the leads (12,13,14, and 15). During the process of encapsulating the leadframe (10), the blocking fulcrums (21,23) restrict encapsulating material from exiting the mold cavity and from attaching to the leads (12,13,14, and 15).
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The present invention relates, in general, to packaging, and more particularly, to methods of forming leadframes and semiconductor packages.
In the past, various methods were utilized to manufacture both semiconductor packages and the leadframes utilized in manufacturing the semiconductor packages. One leadframe manufacturing method produced a leadframe having a dam-bar that extended laterally between the leads and that was connected to each lead of the leadframe. When the leadframe was molded into a package, the dam-bar was intended to prevent the molding compound from reaching the package leads. The dam-bar had to be positioned sufficiently far from the package body to leave room to excise the dam-bar without damaging the package body. The large space between the package body and the dam-bar allowed the mold material to escape and fill the space. The material also attached to the side of the leads.
Another method produced a leadframe that did not have a dam-bar. The molding equipment or mold that was utilized to produce the semiconductor package had channels or recesses into which the leads were placed. During the molding operation, mold material often traveled through the channels and attached to the sides of the leads. This mold material often is referred to as flash or flashing.
The flashing that resulted from these processes had to be removed from the leads after the molding operations were complete. In some cases, the flashing was along the entire length of the lead and could be up to 0.15 millimeters thick. Flash removal procedures included using a high-pressure jet of water or of particles or a chemical jet to remove the flashing. The pressure often was in the range of about two hundred fifty to four hundred twenty five Kilo-grams/square centi-meter (250-425 KGm/cm2).
As the size of semiconductor packages and leads for the packages continued to decrease, the leads and the packages became more delicate and more easily damaged. The smaller lead and package sizes made it more difficult to prevent the mold material from escaping the mold cavities, thus, made it more difficult to keep the mold material from adhering to the leads. In some cases the flashing was longer than the finished lead length and could be thicker than the lead width. This made flashing removal very difficult. Additionally, the smaller lead and package size made it more difficult to remove the flashing without damaging the leads and the packages.
Accordingly, it is desirable to have a leadframe having small leads, that reduces the amount of mold material escaping from the mold cavity and along the leads, that reduces the amount of mold material or flashing adhering to the leads, and that minimizes lead damage during flashing removal.
BRIEF DESCRIPTION OF THE DRAWINGS
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well known steps and elements are omitted for simplicity of the description.
DETAILED DESCRIPTION OF THE DRAWINGS
Site 25, and typically each site 20, of leadframe 10 are also formed to include a plurality of blocking fulcrums that assist in blocking encapsulation material from flowing along the plurality of leads and from attaching to the plurality of leads. The plurality of blocking fulcrums include blocking fulcrums 21 and 22. In general, one of fulcrums 21 or 22 is formed adjacent each side of each lead 12, 13, 14, or 15. Other embodiments may have more than one fulcrum between leads or may have fewer. Although fulcrums 21 and 22 are illustrated with different widths, the width of each blocking fulcrum generally is determined from a number of parameters including the number of leads, lead spacing, and the width of the leads. A proximal end of fulcrums 21 and 22 is attached to panel 11. Fulcrums 21 and 22 have sides 31 that extend from the proximal end toward section 40 and terminate at a distal end 32. Preferably, a distance 30 separates ends 32 from the edge of cavity section 40. However, in some cases, ends 32 may extend a small distance or second distance into section 40. In such a case, ends 32 terminate a shorter distance into section 40 than do the ends of leads 12-15, thus, the first distance of ends 18 is larger than the second distance of ends 32. Distance 30 can be up to about fifty (50) microns and preferably is no greater than about ten (10) microns. For the case where ends 32 extend the second distance into section 40, the second distance generally is no greater than about fifty (50) microns. Sides 31 typically are adjacent to one of leads 12-15 and separated from the adjacent lead by a small spacing 35 (see
As will be seen subsequently, during the process of encapsulating sites 20 of leadframe 10 fulcrums 21 and 22 substantially prevent the flow of encapsulating compound from escaping and attaching to leads 12-15. After the encapsulation process, fulcrums 21 and 22 will be moved away from the plane of leads 12-15 and leadframe 10. In order to facilitate the movement, leadframe 10 may be formed to include optional relief features 36 that assist in controlling any bending or other movement that occurs at the proximal end of fulcrums 21 and 22. Features 36 are illustrated by dashed lines. Typically, features 36 are indentations that are made in the surface of panel 11. As will be seen hereinafter, during the process of forming a semiconductor package from leadframe 10, features 36 provide a location for fulcrums 21 and 22 to move or to bend. This minimizes the deformation of panel 11 and improves the planarity of leads 12-15 as well as the planarity of panel 11. Features 36 are located at the point that is most desirable for fulcrums 21 and 23 to bend or otherwise move. Typically, features 36 are located laterally across fulcrums 21 and 23 at the proximal end of the respective fulcrum. Features 36 have a length that is sufficient to control the movement as desired. In the preferred embodiment, features 36 extend approximately across the width of fulcrums 21 and 22, however, in other embodiments features 36 may only extend a portion of the width of fulcrums 21 and 22.
Referring back to
Subsequent to the molding operation, fulcrums 21 and 22 are moved so that leads 12-15 can be plated. The movement carries sides 31 pass the sides of leads 12-15. Fulcrums 21 and 22 may be moved above or below panel 11, or may be moved both above and below. Distance 30 and spacing 35 are formed to be a size that facilitates such movement without damaging leads 12-15 or body 45. Fulcrums 21 and 22 generally are moved a distance that is sufficient to ensure they do not interfere with subsequent plating operations. For example, if the plating material is plated to a thickness of about ten (10) microns, fulcrums 21 and 22 should be moved at least ten (10) microns. In some cases fulcrums 21 and 22 may be moved up to ninety degrees (90°) or up to about one hundred eighty degrees (180°) to assist in plating the leads and in singulating the package from panel 11.
During the movement of fulcrums 21 and 23, any or all of optional features 36, ports 34, and openings 33 can assist in controlling the movement of fulcrums 21 and 22 to occur at the proximal end so that the majority of fulcrums 21 and 22 remain straight and move without damaging leads 12-15. In some cases, such as distance 30 being too large, moving fulcrums 21 and 23 may also assist in removing some of the encapsulation material or flashing that may be attached to leads 12-15.
After fulcrums 21 and 22 are moved, leadframe 10 is plated. Plating of the leads is well known in the art. Subsequently, the encapsulated package is singulated from panel 11 by cutting leads 12, 13, 14, and 15 to extend a desired length from body 45. This singulation operation typically leaves fulcrums 21 and 22 attached to panel 11. All surfaces of leads 12, 13, 14, and 15 are plated and no bare sections remain. It should also be noted, that some small portions of the encapsulation material may remain on the leads, however, this portion is very small and very thin, thus, any subsequent de-flashing operations can be done much more easily than prior de-flashing operations thereby preventing damage to the leads. For example, a lower pressure water jet may be used at a pressure that is about four or five time less than the pressure of prior high pressure water jet operations. If required, this de-flashing step typically is performed prior to plating. The lower pressure reduces damage to the package and to leads 12, 13, 14, and 15 thereby improving reliability and lowering the manufacturing costs.
Typically, leads 12, 13, 14, and 15 are less than about 0.2 milli-meters wide and less than about 0.1 milli-meters thick. However fulcrums 21 and 22 and spacing 35 can be used to improve leadframes, and packages using the leadframes, having leads that are thicker or wider or thinner or narrower.
Although body 45 is shown with leads 12-15 near the bottom of one side of body 45, those skilled in the art realize that leads 12-15 could be formed on all sides of body 45 and at various locations along the surface of each side.
In view of all of the above, it is evident that a novel device and method is disclosed. Forming a blocking fulcrum adjacent to the sides of the leads facilitates using the blocking fulcrum to restrict mold material from reaching the leads. Making the spacing between the leads and the blocking fulcrums very small substantially prevents encapsulating compound from traveling along the sides of the leads and substantially prevents flashing on the leads. Although described with a transfer molding operation, the leadframe and method is also applicable to injection molding.
Claims
1. A method of forming a leadframe for a semiconductor device comprising:
- forming a leadframe strip having a main panel and a plurality of cavity sections;
- forming a plurality of leads extending from the main panel a first distance into a cavity section of the plurality of cavity sections;
- forming three sides of each of the plurality of leads detached from the main panel and forming a proximal end of each of the plurality of leads attached to the main panel; and
- forming a blocking fulcrum extending from the main panel adjacent to a side of a lead of the plurality of leads and detached from the side of the lead of the plurality of leads and including terminating the blocking fulcrum no greater than a second distance from the cavity section.
2. The method of claim 1 wherein forming the blocking fulcrum extending from the main panel includes forming the blocking fulcrum to extend less than the first distance into the cavity section.
3. The method of claim 1 wherein forming three sides of each of the plurality of leads detached from the main panel includes cutting at least one side of at least one lead of the plurality of leads away from the blocking fulcrum.
4. The method of claim 3 further including realigning the blocking fulcrum and the least one lead of the plurality of leads subsequent to cutting the at least one side of at least one lead of the plurality of leads away from the blocking fulcrum.
5. The method of claim 1 further including forming a relief feature extending laterally across a portion of a width of the blocking fulcrum near the proximal end of the blocking fulcrum.
6. The method of claim 5 further including forming the relief feature having a shape that is one of a V shape or a U shape.
7. The method of claim 1 further including forming a relief port through the main panel near the proximal end of the blocking fulcrum including forming the relief port having a shape that is one of a circle, a square, a rectangle, or a triangle.
8. The method of claim 7 further including forming a relief opening through the main panel near the proximal end of the side of the lead of the plurality of leads.
9. The method of claim 1 wherein forming the blocking fulcrum extending from the main panel adjacent to the side of the lead of the plurality of leads and detached from the side of the lead of the plurality of leads and including terminating the blocking fulcrum no greater than the second distance from the cavity section includes forming the second distance no greater than 50 microns.
10. A method of forming a semiconductor package from a leadframe comprising:
- providing the leadframe having leads and having a blocking fulcrum extending from a main panel of the leadframe toward a cavity section of the leadframe;
- encapsulating the cavity section of the leadframe to form a body; and
- moving the blocking fulcrum away from a plane of the leads and away from the body.
11. The method of claim 10 further including plating the leads of the semiconductor package.
12. The method of claim 10 further including singulating the body and the leads from the main panel and the blocking fulcrum.
13. The method of claim 10 wherein moving the blocking fulcrum away from the plane of the leads includes bending the blocking fulcrum.
14. A leadframe for a semiconductor package comprising:
- a leadframe strip having a main panel and a plurality of cavity sections;
- a plurality of leads having a proximal end attached to the main panel and having sides extending from the main panel a first distance into a cavity section of the plurality of cavity sections, the sides detached from the main panel; and
- a blocking fulcrum extending from the main panel toward the cavity section, the blocking fulcrum detached from the sides and terminating no greater than a second distance from the cavity section.
15. The leadframe of claim 14 wherein the blocking fulcrum extending from the main panel toward the cavity section includes the blocking fulcrum being spaced from the sides.
16. The leadframe of claim 15 wherein the blocking fulcrum being spaced from the sides includes the blocking fulcrum spaced no more than about 25 microns from the sides.
17. The leadframe of claim 14 further including a relief opening through the main panel where the sides intersect the main panel.
18. The leadframe of claim 14 further including an indentation extending across a portion of the blocking fulcrum where the blocking fulcrum intersects the main panel.
19. The leadframe of claim 14 wherein the blocking fulcrum extending from the main panel toward the cavity section includes the blocking fulcrum extending adjacent to at least one side of the sides.
20. The leadframe of claim 14 wherein the second distance is no greater than approximately fifty microns.
Type: Application
Filed: Aug 11, 2003
Publication Date: Feb 17, 2005
Applicant:
Inventors: Guan Quah (Gilbert, AZ), Darrell Truhitte (Phoenix, AZ)
Application Number: 10/638,181