Circuit Board Shape Retention During BGA Solder Reflow
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Solution Overview
Problem
Circuit boards tend to warp during solder reflow, leading to broken or incomplete electrical connections in ball grid array (BGA) systems, as the substrate may peel away from the circuit board, causing electrical shorts or failure in connections.
Innovation Solution
The system employs metal balls that do not collapse under predefined forces and temperatures, combined with a fixture that applies force evenly across the substrate to maintain its shape during heating, using solder and conductive contacts to ensure stable electrical connections between the substrate and circuit board.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the substrate is heated during solder reflow, then the solder melts and forms electrical connections, but the substrate warps and peels away from the circuit board
Solution Approach 1:
The patent applies a downward force on the substrate during solder reflow to counteract the upward warping force generated by thermal expansion. This counterbalancing force prevents the substrate from peeling away from the circuit board while allowing the solder to melt and form connections.
Solution Approach 2:
The patent modifies the mechanical parameters of the substrate system by applying controlled force during the thermal process. The force magnitude and distribution are adjusted to maintain substrate flatness across different temperature conditions, transforming a thermal problem into a mechanically controlled process.
2Shape
If force is applied to maintain substrate shape, then warping is prevented, but metal balls may collapse under the force and temperature
Solution Approach 1:
The patent specifies that metal balls must be pre-formed with sufficient structural strength before the solder reflow process. The metal balls are designed and prepared in advance to withstand the combined thermal and mechanical stresses that will occur during the connection process, preventing collapse before it can occur.
Solution Approach 2:
The patent employs metal balls made from composite or alloy materials that combine high melting point properties with high mechanical strength. These composite materials allow the metal balls to resist both the thermal softening and the compressive forces applied during substrate flattening.
3Reliability
If the substrate peels away from the circuit board, then electrical connections are broken or incomplete, but applying force to prevent peeling may cause metal ball collapse
Solution Approach 1:
The metal balls are pre-engineered with adequate structural strength to withstand the forces applied during the connection process. This preliminary design ensures that when force is applied to maintain substrate contact and ensure reliable electrical connections, the metal balls do not collapse.
Solution Approach 2:
The use of composite or alloy materials in metal ball construction provides both the thermal resistance needed to prevent melting and the mechanical strength needed to prevent collapse under compressive force, thereby ensuring reliable electrical connections.
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 configuration reduces the likelihood of substrate warping, maintains flatness, and prevents electrical shorts by ensuring metal balls remain stable and do not collapse, thus ensuring reliable electrical connections across the circuit boards even at elevated temperatures.
Implementation Method 1
metal balls that are configured not to collapse in whole or part in response to a force below a predefined force and a temperature below a predefined temperature
Implementation Method 2
The system may include solder between at least some of the metal balls and conductive contacts on the circuit board
Data Source
AI summary
An example system for maintaining the shape of a circuit board includes metal balls that are configured not to collapse in whole or part in response to a force below a predefined force and a temperature below a predefined temperature. The metal balls are configured to support a substrate and are part of electrical connections between the substrate and a circuit board. The system includes a fixture configured to apply force to the substrate while the substrate is subjected to the temperature. The fixture is configured to distribute the force across a surface of the substrate that is not in contact with the metal balls such that the force applied by the fixture and the support of the substrate by the metal balls maintains a shape of the substrate at the temperature.