Control of under-fill using an encapsulant and a trench or dam for a dual-sided ball grid array package

Abstract

Disclosed herein are methods of fabricating a packaged radio-frequency (RF) device. The disclosed methods use an encapsulant on solder balls in combination with a dam or a trench to control the distribution of an under-fill material between one or more components and a packaging substrate. The encapsulant can be used in the ball attach process. The fluxing agent leaves behind a material that encapsulates the base of each solder ball. The encapsulant reduces the tendency of the under-fill material to wick around the solder balls by capillary action which can prevent or limit the capillary under-fill material from flowing onto or contacting other components. The dam or trench aids in retaining the under-fill material within a keep out zone to prevent or limit the under-fill material from contacting other components.

What is claimed is: 
     
         1 . A method of fabricating a packaged radio-frequency (RF) device, the method comprising:
 mounting electrical components to a first side of a packaging substrate;   forming a dam on a second side of the packaging substrate;   attaching solder balls to the second side of the packaging substrate;   encapsulating the solder balls with an encapsulant;   attaching a lower electrical component to the second side of the packaging substrate; and   under-filling the lower electrical component mounted with an under-filling agent such that the under-filling agent contacts the encapsulant or contacts the dam.   
     
     
         2 . The method of  claim 1  wherein the encapsulant is a polymer. 
     
     
         3 . The method of  claim 1  wherein the encapsulant is not removed in a cleaning process following attachment of the solder balls to the packaging substrate. 
     
     
         4 . The method of  claim 1  wherein the encapsulant forms an obtuse angle with the packaging substrate. 
     
     
         5 . The method of  claim 1  wherein the encapsulant forms an obtuse angle to the solder balls. 
     
     
         6 . The method of  claim 1  wherein the under-filling agent contacts the encapsulant and not the solder balls. 
     
     
         7 . The method of  claim 1  wherein the combination of the dam and the encapsulant is configured to limit the distribution of the under-fill material to maintain the under-fill material a targeted distance from the solder balls while providing targeted coverage under and around the lower electrical component. 
     
     
         8 . The method of  claim 1  wherein the dam is closer to the lower electrical component than the encapsulant. 
     
     
         9 . The method of  claim 8  wherein the under-fill material contacts the dam prior to contacting the encapsulant. 
     
     
         10 . The method of  claim 1  wherein the encapsulant is configured to reduce capillary action causing the under-fill material to wick around the solder balls. 
     
     
         11 . A method of fabricating a packaged radio-frequency (RF) device, the method comprising:
 mounting electrical components to a first side of a packaging substrate;   forming a trench on a second side of the packaging substrate;   attaching solder balls to the second side of the packaging substrate;   encapsulating the solder balls with an encapsulant;   attaching a lower electrical component to the second side of the packaging substrate; and   under-filling the lower electrical component mounted with an under-filling agent such that the under-filling agent contacts the encapsulant or at least partially fills the trench.   
     
     
         12 . The method of  claim 11  wherein the encapsulant is a polymer. 
     
     
         13 . The method of  claim 11  wherein the encapsulant is not removed in a cleaning process following attachment of the solder balls to the packaging substrate. 
     
     
         14 . The method of  claim 11  wherein the encapsulant forms an obtuse angle with the packaging substrate. 
     
     
         15 . The method of  claim 11  wherein the encapsulant forms an obtuse angle to the solder balls. 
     
     
         16 . The method of  claim 11  wherein the under-filling agent contacts the encapsulant and not the solder balls. 
     
     
         17 . The method of  claim 11  wherein the combination of the trench and the encapsulant is configured to limit the distribution of the under-fill material to maintain the under-fill material a targeted distance from the solder balls while providing targeted coverage under and around the lower electrical component. 
     
     
         18 . The method of  claim 11  wherein the trench is closer to the lower electrical component than the encapsulant. 
     
     
         19 . The method of  claim 18  wherein the under-fill material fills the trench prior to contacting the encapsulant. 
     
     
         20 . The method of  claim 11  wherein the encapsulant is configured to reduce capillary action causing the under-fill material to wick around the solder balls.