Maintaining the shape of a circuit board

A system comprising:

• 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 being configured to support a substrate, the metal balls being part of electrical connections between the substrate and a circuit board;
• and
• a fixture having a size that enables application of force to an entire a surface of the substrate at once while the substrate is subjected to the temperature, the fixture being configured to distribute the force across a flat surface of the fixture in contact with the 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;
• wherein the substrate comprises one or more components on a surface of the substrate;
• and
• wherein the fixture comprises indentations that complement shapes of the one or more components but that do not produce contact between the fixture and the one or more components.