Solder Paste Die Attach

Epoxy-Speed Placement, Solder-Grade Thermal Performance

Solder paste die attach, or reflow attach, uses solder paste to attach SMT components. It can be processed at the same speed as epoxy die attach, yet provides the high thermal conductivity components need to function correctly. Solder paste comes in wide varieties, with solder type, shape, and size varying by formulation. Typical solder pastes are suspensions of tiny solder balls in flux that reflow and create a solder joint when brought to the proper temperature.

Process Control From Dispense to Reflow

Like epoxy, components placed into solder paste can maintain their position throughout handling and can be reflowed in a batch oven. However, an inert environment is essential to create a good bond. Solder reflow profiles also need to incorporate time before the reflow point to "burn off" the flux that suspends the solder balls.

Solder paste is mainly deposited through dispensing, using time-pressure, auger pump, or jetting methods. Once dispensed, the solder spreads out slightly due to the flux. At reflow temperature, it pulls in and bonds only to the gold surfaces of the board or ceramic, forming strong structural bonds that can "reach" up the sides of the components. Solder paste generally reflows at a higher temperature than epoxies cure.

Equipment_Handler_With_Package_3880_TurretR-1

Solder Paste Die Attach for Flip-Chip Applications

Solder paste die attach can also be used effectively for flip-chip applications, where the solder surrounds the joint between the bumps and pads to create a secure connection.

The trade-off of this movement and tightening is that some of the original placement accuracy may be lost. In most cases, this isn't a concern, since applications that tolerate this movement typically don't have tight placement-accuracy requirements.