Backside encapsulation of tape automated bonding device

A TAB device (10) is coupled to a circuit board (12). The TAB device (10) includes a semiconductor die (11) having leads (18) extending therefrom. A material layer (30), typically a polyimide layer, covers the inward portion of the leads (18) to maintain leading position during attachment of the TAB device (10) to the circuit board (12). Prior to attachment, a backside encapsulation region (40) is applied to the backside of the TAB device (10), sealing the backside of the leads (18). The backside encapsulation material is selected to have a coefficient of thermal expansion similar to the coefficient of thermal expansion of the first material layer (18). The backside encapsulation material is selected to have a coefficient of thermal expansion similar to the coefficient of thermal expansion of the first material layer (30), to prevent excessive warpage. During attachment, migration of the die attach layer (22) towards the leads will be stopped by the backside encapsulation region (40), preventing the die attach material from shorting the leads (18) of the device (10).

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What is claimed is:

1. A method of making a tape automated bonding (TAB) device, comprising the steps of:

providing a semiconductor die having circuitry formed therein;

coupling a plurality of leads to said semiconductor die, said leads having first and second surfaces;

applying a first material layer having a known coefficient of thermal expansion to a first surface of the leads in order to maintain the positioning of the leads; and

applying a second material layer having a coefficient of thermal expansion within a predetermined range of the coefficient of thermal expansion of said first material layer to a second surface of the leads.

2. The method of claim 1, wherein said step of applying a first material layer comprises the step of applying a polyimide material to said first surface of the leads.

3. The method of claim 2, wherein said step of applying a second material layer comprises the step of applying a polymer adhesive material to said second surface of said leads.

4. The method of claim 3, wherein said step of applying a polymer adhesive material comprises the step of applying a mixture of epoxy and silica particles to said second surface of said leads.

5. The method of claim 4, wherein said step of applying a mixture of epoxy and silica particles comprises the step of applying a mixture of polymers and silica particles having a coefficient of thermal expansion of 15 to 22.times.10.sup.-6 per.degree. C.

6. The method of claim 5, and further comprising the step of heating said first material layer prior to said step of applying said second material layer.

7. The method of claim 6, wherein said heating step comprises the step of heating said first material layer to 50-110.degree. C.

8. The method of claim 1, further comprising a step of applying a layer of conductive die attach material having an area approximately equal to the area of the die.

9. The method of claim 1, wherein said second material layer extends onto at least one side surface of said die.

10. The method claim 9, wherein a die attach layer is formed on said semiconductor die and at least a portion of said second material layer.

11. A method, comprising:

providing a circuit board;

providing a semiconductor die having circuitry formed therein, coupling said semiconductor die to said circuit board via a plurality of leads, said leads having first and second surfaces;

applying a first material layer having a known coefficient of thermal expansion on said first surface of said leads to maintain the positioning of said leads; and

applying a second material layer having a coefficient of thermal expansion within a predetermined range of said known coefficient of thermal expansion disposed on said second surface of said leads.

12. The method of claim 11, wherein said second material layer has a coefficient of thermal expansion similar to the coefficient of thermal expansion of the first material layer.

13. The method of claim 11, wherein said second material layer encapsulates said second surface of said leads.

14. The method of claim 11, wherein said die attach layer is formed on said semiconductor die and at least a portion of said second material layer.

15. The method of claim 11, wherein said die attach layer provides an electrical connection between said die and said circuit board.

16. The method of claim 11, wherein said electrical connection is for grounding purposes.

17. The method of claim 11, wherein said die attach layer provides a thermal path for dissipating heat from said die to said circuit board.

18. The method of claim 11, wherein said die attach layer provides an electrical and thermal connection between said die and said circuit board.

19. The method of claim 11, wherein said first material layer comprises a polyimide material and said second material layer comprises a polymer material.

20. The method of claim 19, wherein said polymer layer comprises an epoxy layer filled with silica.

21. The method of claim 20, wherein said epoxy layer filled with silica comprises an epoxy layer having a silica filler content between 67 an 72%.

22. The method of claim 11, wherein said second material layer extends onto at least one side surface of said die.

23. The method of claim 22, further comprising a die attach layer which is formed on said semiconductor die and at least a portion of said second material layer.