Solder Bump Maker Paste for Fine Pitch PCB Soldering
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Solution Overview
Problem
Existing methods struggle to evenly apply solder paste on fine pitch metal pads with pitches of 130 μm or less due to deteriorated spreading properties, making it difficult to form low volume solder on pads on PCBs, which is crucial for refining copper circuit patterns in small and slim electronic devices.
Innovation Solution
A method involving the application of a solder bump maker paste with a predetermined thickness to the entire surface of a PCB, including a metal pad and solder mask, followed by heating and cooling to form a low volume solder on pad, and subsequent washing of residual polymer resin and solder particles using a solvent, facilitating flip chip bonding of semiconductor devices with copper pillars.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a metal mask for screen printer is used to apply solder paste on metal pad, then the solder paste can be applied to metal pad portion, but when pitch is 130 μm or less, the spreading property of solder paste from mask is deteriorated and it becomes difficult to evenly apply predetermined quantity of solder paste
Solution Approach 1:
The patent changes the physical and chemical parameters of the solder application material from traditional solder paste to solder bump maker paste with specific composition (solder particles 50-80 wt%, organic vehicle 20-50 wt%). This parameter change enables the material to maintain its shape without spreading on fine pitch pads while still being applicable through screen printing process.
Solution Approach 2:
The patent uses a solder bump maker paste that replicates the function of solder paste but with different material properties. The paste contains solder particles suspended in an organic vehicle that prevents spreading, effectively copying the solder application function while solving the fine pitch problem.
2Productivity
If traditional solder paste application method is used on fine pitch PCB, then the process can be completed, but the solder paste cannot be evenly applied and predetermined quantity cannot be controlled on metal pad
Solution Approach 1:
The patent modifies the material parameters by using solder bump maker paste with controlled viscosity and composition ratios. The organic vehicle content (20-50 wt%) is specifically controlled to prevent spreading while maintaining applicability, enabling both process completion and precise quantity control on fine pitch pads.
Solution Approach 2:
The patent uses a consumable solder bump maker paste that is applied and then removed after transferring solder particles to the pad. The organic vehicle and polymer resin are designed to be washable away, leaving only the solder particles on the pad.
3Reliability
If solder mask is formed on fine pitch metal pad to position metal pad lower than surface, then concave shape is formed, but it becomes more difficult to evenly apply solder paste with predetermined thickness
Solution Approach 1:
The patent changes the rheological parameters of the application material to match the concave pad geometry. The solder bump maker paste is formulated with specific viscosity and flow characteristics that enable it to fill concave areas uniformly without bridging between adjacent pads, achieving both accurate pad positioning and uniform solder distribution.
4Ease of manufacture
If screen printer with metal mask is used for solder paste application, then solder paste can be applied to metal pad, but the spreading property deteriorates on fine pitch and even application becomes difficult
Solution Approach 1:
The patent modifies the material parameters of the solder application substance by using solder bump maker paste with controlled particle size distribution, organic vehicle composition, and polymer resin content. These parameter changes enable the material to be applied through screen printing while preventing unwanted spreading, achieving both ease of manufacture and distribution uniformity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enables the easy formation of low volume solder on pads on fine pitch PCBs, preventing electrical connections between adjacent solders during flip chip bonding, ensuring reliable bonding and maintaining uniformity even under pressure.
Implementation Method 1
heating the SBM paste at a temperature higher than a melting point of solder contained in the SBM paste and then cooling the SBM paste to form a solder on pad
Implementation Method 2
heating the SBM paste at a temperature higher than a melting point of solder contained in the SBM paste and then cooling the SBM paste to form a solder on pad
Implementation Method 3
washing a residual polymer resin and residual solder particles of the SBM paste by using a solvent
Data Source
AI summary
Disclosed are a method of forming a solder on pad on a fine pitch PCB and a method of flip chip bonding a semiconductor device using the same. The method of forming a solder on pad on a fine pitch PCB includes: applying a solder bump maker (SBM) paste with a predetermined thickness to an entire surface of a PCB including a metal pad and a solder mask; heating the SBM paste at a temperature higher than a melting point of solder contained in the SBM paste and then cooling the SBM paste to form a solder on pad; and washing a residual polymer resin and residual solder particles of the SBM paste by using a solvent.