Forming low stress joints using thermal compress bonding

A method comprising:

• placing a second work piece over a first work piece, wherein the first work piece comprises:
• a first dielectric layer having a top surface;
• and
• a first solder bump having a first portion over the first dielectric layer, and a second portion extending into the first dielectric layer, and wherein the second work piece comprises a second solder bump at a surface, and wherein the first and the second solder bumps contact each other;
• placing a heating tool contacting the second work piece;
• heating the second work piece using the heating tool to melt the first and the second solder bumps to form a third solder bump;
• and
• before the third solder bump solidifies, pulling up the second work piece, until an angle formed between a tangent line of the second solder bump and the top surface of the dielectric layer is greater than about 50 degrees, wherein the tangent line is drawn starting from a joint of the third solder bump and the dielectric layer.