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High SJR BGA Package Design

IP.com Disclosure Number: IPCOM000244834D
Publication Date: 2016-Jan-20
Document File: 4 page(s) / 433K

Publishing Venue

The IP.com Prior Art Database

Abstract

Current BGA package SJR is a cause of high concern for SMT applications. In some cases, ball break occurs "between ball and substrate" or "between ball and PCB". This is a fatal constraint for BGA applications, especially for automotive applications. To improve BGA SJR capability, SMT customers sometimes put a film around the BGA. During reflow, the film melts and flows into the solder balls clearance through capillary effect. This method can improve BGA SJR relatively, but it has weaknesses, such as (i) fill-in can't attain 100% coverage for all ball areas, (ii) to increase coverage requires a long time, since melted film flow is very slow, and (iii) more PCB space must be reserved to arrange film location, otherwise the film can't be put in.

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High SJR BGA Package Design

Background: 

Current BGA package SJR is a cause of high concern for SMT applications.  In some cases, ball break occurs “between ball and substrate” or “between ball and PCB”.  This is a fatal constraint for BGA applications, especially for automotive applications.  To improve BGA SJR capability, SMT customers sometimes put a film around the BGA.  During reflow, the film melts and flows into the solder balls clearance through capillary effect.  This method can improve BGA SJR relatively, but it has weaknesses, such as (i)  fill-in can’t attain 100% coverage for all ball areas, (ii)  to increase coverage requires a long time, since melted film flow is very slow, and (iii) more PCB space must be reserved to arrange film location, otherwise the film can’t be put in.

Body:   

In this paper we present an assembly method that can overcome the above three weaknesses in the apply film design.  We integrate B-stage adhesive into the package design.  The method realizes 100% ball coverage with adhesion material and improves SJR for BGA package.  Before reflow, all B-stage adhesive material will remain at spaces between the solder balls, applied using a screen printing process. After reflow, the B-stage adhesive material melts and flows through the balls and stays between the substrate and the PCB.  We use a B-stage adhesive with low reactivity curing agent.  The B-stage adhesive can be partially cured (“pre-dried”) at an initi...