SEMICONDUCTOR PACKAGE WITH INDIVIDUALLY MOLDED LEADFRAME AND DIE COUPLED AT SOLDER BALLS
According to principles as taught herein, a leadframe array for a semiconductor die is prepared having locations to receive solder balls. Solder balls are then applied to the leadframe array, after which the leadframe array and solder ball combination is placed in a first mold and encased in a first molding compound. After the molding compound is cured, a layer of molding compound is removed to expose the solder balls. After this, a semiconductor die is electrically connected to the exposed solder balls. The combined semiconductor die and leadframe are placed in a second mold, and a second molding compound injected. The second molding compound flows around the semiconductor die and leadframe combination, fully enclosing the electrical connections between the leadframe and the semiconductor die, making the final package a twice-molded configuration. After this, the twice-molded semiconductor package array is cut at the appropriate locations to singulate the packages into individual products.
This disclosure is in the field of semiconductor packages, and in particular, is directed towards a semiconductor package in which the leadframe and semiconductor package are each molded separately, then are joined together with solder balls.
Description of the Related ArtSemiconductor packages must protect the semiconductor die from the external environment while providing an output at the electrical signals for use by other circuits. The package, therefore, must be sufficiently protective and robust to prevent damage to the semiconductor die, while at the same time providing electrical connections so the signals may be received by and sent out from the semiconductor die.
Traditionally, a semiconductor die is placed on a leadframe or other substrate, and it is then electrically connected to this leadframe by bonding wires, solder balls, or other electrical coupling. After this, the combination is placed in a mold, and a molding compound injected into the mold to fully encase the die, but leave some of the electrical connections exposed so that it may be connected to the outside environment. Such an approach, while beneficial in many circumstances, has the goal of securely enclosing the semiconductor die while at the same time ensuring there is exposure to the electrical connections that extend away from the semiconductor die. Improvements in the packaging process, and the end package itself, will provide the benefit of greater reliability in the operation over the longer term use of the die, as well as having fewer failures during the semiconductor packaging process.
BRIEF SUMMARYAccording to principles as taught herein, a leadframe array for a semiconductor die is prepared having locations to receive solder balls. Solder balls are then applied to the leadframe array, after which the leadframe array and solder ball combination is placed in a first mold and encased in a first molding compound. In one embodiment, the solder balls are fully encased in molding compound so as to be completely surrounded by the molding compound.
After the molding compound is cured, a layer of molding compound is removed to expose the solder balls. After this, a semiconductor die is electrically connected to the exposed solder balls. The combined semiconductor die and leadframe are placed in a second mold, and a second molding compound injected. The second molding compound flows around the semiconductor die and leadframe combination, fully enclosing the electrical connections between the leadframe and the semiconductor die, making the final package a twice-molded configuration. After this, the twice-molded semiconductor package array is cut at the appropriate locations to singulate the packages into individual products.
The present method permits the leadframe array to be fully constructed, encapsulated, and provided with electrical connections in a separate manufacturing line, prior to the introduction of the semiconductor die. Only after the leadframe array is encapsulated is the semiconductor die connected to the leadframe, thus providing a more rapid, and lower cost, technique for attaching the die to the leadframe. The leadframe is an array of leadframes, having many hundreds, or many thousands, of positions for a die. Accordingly, the package can be mass-produced with thousands of semiconductor die attached to the array of leadframes, after which the combination is placed in a second mold, encapsulated in a second molding compound and then singulated.
As can be seen in
In the embodiment of
The package 11, as shown in
The low-profile package 11, as shown in
Alternatively, if an ultrathin, extremely low-profile package 11 is desired, then the removal of the package can continue significantly past when the semiconductor die 12 is exposed, to remove substantial portions of the semiconductor die 12, together with the molding compound 27. Namely, the blanket removal of the top side of the package can continue to remove a significant height of the semiconductor die 12 along with the molding compound 27 to substantially reduce the profile of the overall package. In this embodiment, an ultrathin package can be obtained, in which the semiconductor die 12 has approximately half or even one-third of its standard height, and the molding compound 27 is flush with the top of the semiconductor die 12 in the final ultrathin package 11, as shown in
The embodiment of
Layer 20 is applied as a blanket layer to the exposed surface of the leadframe 18 and patterned and etched to a desired pattern as shown in
The removal of the molding compound 24 and the top portion of each solder ball 22 can be achieved by any acceptable technique, milling being a preferred technique. It can also be removed using sawing, polishing, etching (either wet etching or dry etching), grinding, or other acceptable technique in order to remove the upper portion of molding compound 24 along with a portion of each solder ball 22.
The combined semiconductor die 12 and once molded leadframe 18 are placed in a second mold. After being placed in the second mold, a second molding compound 16 is injected into the second mold to fully encase the semiconductor die 12 and also to bond with the first molding compound 24. The second molding compound 16 is selected which will strongly adhere to and firmly mold to the first molding compound 24. In some embodiments, the second molding compound 16 may become a unitary, contiguous molding compound with the first molding compound 24 at their junction such that the line between them is virtually invisible and indistinguishable. The twice-molded assembly is provided by taking the first-molded leadframe 18 having the first molding compound 24 thereon and placing it into a second mold and then subjecting it to a second molding step, with the semiconductor die 12 attached in order to encapsulate a second time the leadframe 18 and for a first time the semiconductor die 12.
After the second molding step as shown in
In one alternative embodiment, the reflow step is carried out when the assembly is in the condition as shown in
In one preferred embodiment, the reflow occurs in two separate steps. In a first step, a first, minimal reflow is carried out when solder bump 14 is first brought into contact with solder ball 22 in order to adhere the two solder balls to each other and provide a strong mechanical and electrical connection. A first, minimum temperature reflow occurs by slight heating of the leadframe 18 with the solder ball 22 attached so that upon the solder bumps 14 touching the heated solder balls 22 there is a slight merge between the solder balls bringing them into strong mechanical and electrical connection. Preferably, this initial connection is carried out just as the semiconductor die 12 is first placed on the leadframe array 18 as shown in
If the high temperature reflow were carried out when the assembly is partially completed as shown in
In the stages shown in
After the second reflow is carried out, the leadframe 18 is etched on the back side with an etching fluid that is selective to remove the leadframe material 18, but not remove the metal layer 20. Preferably, the leadframe 18 is made of copper, or in one embodiment aluminum. A wet etch which selectively removes copper, but does not remove nickel or a nickel, palladium, gold layer combination is used. This wet etch will remove the exposed copper portions of leadframe 18 so that some of the molding compound 24 protrudes through the bottom of the package, as can be seen in
Multiple embodiments have been shown for creating a twice-molded semiconductor package 10. The various embodiments may be combined with each other to achieve a wide variety of different packages according to the various alternative embodiments as taught herein.
The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments.
These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.
Claims
1. A method for making a semiconductor die package, comprising:
- forming recesses in a first surface of a leadframe array;
- placing solder in the recesses of the leadframe array to form solder balls;
- placing the combined leadframe array and solder balls into a mold;
- injecting a molding compound into the mold sufficient to fully encapsulate the solder and the first surface of the leadframe array to create a once-molded leadframe array;
- removing an upper portion of the molding compound and the solder balls sufficient to expose an interior surface area of the solder;
- attaching a semiconductor die to the exposed solder;
- placing the combined semiconductor die and once-molded molded leadframe array into a second mold;
- injecting a second molding compound into the second mold to encapsulate the semiconductor die and the upper surface of the exposed first molding compound; and
- singulating individual semiconductor die packages from the twice-molded semiconductor package array.
2. The method of claim 1, further including:
- attaching a solder ball to the semiconductor die prior to connecting the die to the once-molded leadframe array.
3. The method according to claim 2 wherein the connection of the semiconductor die to the once-molded leadframe array includes the step comprising:
- bringing the solder connected to the semiconductor die into physical contact with the solder of the once-molded leadframe array.
4. A method for making a semiconductor die package, comprising:
- forming recesses in a first surface of a leadframe array;
- placing solder in the recesses of the leadframe array to form solder balls;
- placing the combined leadframe array and solder balls into a mold;
- injecting a molding compound into the mold sufficient to fully encapsulate the solder and the first surface of the leadframe array to create a once-molded leadframe array;
- removing an upper portion of the molding compound and the solder balls sufficient to expose an interior surface area of the solder;
- attaching a solder ball to a semiconductor die;
- attaching the semiconductor die to the exposed solder after connecting the die to the once-molded leadframe array by bringing the solder connected to the semiconductor die into physical contact with the solder of the once-molded leadframe array;
- placing the combined semiconductor die and molded leadframe array into a second mold;
- injecting a second molding compound into the second mold to encapsulate the semiconductor die and the upper surface of the exposed first molding compound to create a twice-molded semiconductor die package array;
- heating the twice-molded semiconductor die array to a sufficient temperature to reflow the solder to merge the solder ball coupled to the die to the solder ball of the once-molded leadframe array to obtain an integral solder coupling between the semiconductor die and the leadframe; and
- singulating individual semiconductor die packages from the twice-molded semiconductor die package array.
5. The method according to claim 4 wherein the heating step is carried out prior to the semiconductor die being placed in the second mold and second molding compound injected therein.
6. The method according to claim 4 wherein the heating step is carried out after the semiconductor die has been removed from second the mold and second molding compound encapsulating it has been cured.
7. The method according to claim 5, further comprising:
- subjecting the solder coupled to the semiconductor die to a first temperature in the heating step to mechanically and electrically affix the solder of the die to the solder of the once-molded leadframe array; and
- subsequently carrying out the step of placing the semiconductor die and leadframe in the second mold and injecting the second molding compound, after which a second reflow temperature is carried out by subjecting the twice-molded semiconductor package array to a second temperature higher than the first temperature to carry out a second reflow to more completely combine the solder ball of the semiconductor die with the solder ball of the leadframe array.
8. The method according to claim 1 wherein the second molding compound fully encapsulates the semiconductor die and the exposed portions of the once-molded leadframe array.
9. The method according to claim 1 wherein the second molding compound fully encapsulates the electrical connection between semiconductor die and the once-molded leadframe array without encapsulating one full surface of the semiconductor die.
10. The method according to claim 1 wherein the second molding compound fully encapsulates the electrical connection between the semiconductor die and the once-molded leadframe array, but does not encapsulate side walls or an exposed surface of the semiconductor die.
11. A semiconductor package comprising:
- a leadframe having a first side and a second side, the lead frame including a lead;
- a first solder member connected to the first side of the lead;
- a first molding compound extending from the first side of the lead, the first molding compound encapsulating the first solder member and the first side of the lead;
- a semiconductor die having an electrical pad on a first surface thereon;
- a second solder member connected to the electrical pad of the semiconductor die and to the first solder member that provides an electrical connection from the semiconductor die to the lead of the leadframe; and
- a second molding compound that encapsulates the semiconductor die, the second solder member and is in direct physical contact with both the second solder member and the first molding compound.
12. The semiconductor package of claim 11 wherein the first solder member is a solder ball.
13. A semiconductor package comprising
- a leadframe having a first side and a second side, the leadframe including a lead;
- a first solder member connected to the first side of the lead;
- a first molding compound extending from the first side of the lead, the first molding compound encapsulating the first solder member and the first side of the lead;
- a semiconductor die having an electrical pad on a first surface thereon;
- a second solder member connected to the electrical pad of the semiconductor die and to the first solder member that provides an electrical connection from the semiconductor die to the lead of the leadframe; and
- a second molding compound that encapsulates the semiconductor die, the second solder member and is in direct physical contact with the first molding compound
- wherein first solder member and the second solder member have been bonded to each other in a heat treatment to form a single, contiguous solder member.
14. The semiconductor package of claim 11 wherein the first molding compound and the second molding compound are comprised of different materials.
15. The semiconductor package of claim 11 wherein the second molding compound encapsulates the sidewalls and the first surface of the semiconductor die but not a second surface of the semiconductor die that is opposite the first surface.
16. The semiconductor package of claim 11 wherein the second molding compound encapsulates the first surface of the semiconductor die but not the sidewall or a second surface of the semiconductor die that is opposite the first surface.
17. A semiconductor package comprising:
- a leadframe having a first side and a second side, the lead-frame including a plurality of leads;
- a plurality of solder balls, one solder ball of the plurality being connected to the first side of each of the respective leads of the plurality of leads;
- a first molding compound connected to the first side of the lead, the first molding compound encapsulating each of the solder balls and the first side of each lead;
- a semiconductor die having a plurality of electrical pads thereon;
- a plurality of solder members connected to each respective electrical pad of the semiconductor die and also to respective solder balls, the solder members and solder balls forming single, contiguous metal connection between the semiconductor die and the leadframe; and
- a second molding compound that encapsulates the semiconductor die, the second solder member and is in direct physical contact with both the solder members and the first molding compound.
18. The semiconductor package of claim 17 wherein the first molding compound and the second molding compound form a unitary, contiguous molding compound.
19. The semiconductor package of claim 17 wherein the solder balls and the solder members are comprised of the same metal alloy.
20. The semiconductor package of claim 17 wherein at least two of the solder balls are connected to the same lead to electrically connect the two solder balls and two of the electrical pads on the semiconductor to each other.
21. The method according to claim 4 wherein the heating step is carried out concurrently with the step of injecting a second molding compound into the second mold to encapsulate the semiconductor die and the upper surface of the exposed first molding compound to create a twice-molded semiconductor die package array.
Type: Application
Filed: Jul 28, 2017
Publication Date: Jan 31, 2019
Inventor: Jefferson TALLEDO (Calamba)
Application Number: 15/663,624