Soldering guidelines

Introduction

Reflow soldering is the most common way of attaching Solid State Optronics (SSO) devices to PCBs. Recommendations for reflow and other means of component attachment to PCBs appear below. For more details on soldering methods, reference Application Note 103 (PDF).

Reflow Soldering

The process of reflow soldering passes a PCB assembly through an oven where solder paste is heated, reflows, and bonds the joint between component leads and PCB contact pads. The assembly is then cooled completing the process. The following figure and table show SSO recommendations for reflow profiles.

Figure 01: Pb-free SMT reflow profile (not to scale). Temperature against time, rising through a preheat and soak phase, past the liquidus temperature to a peak, then cooling. The values are tabulated below.

Profile parameter	Value
Peak Reflow Temperature (TP)	260°C
Time at Peak Temperature (tPmax)	10 seconds
Time within 5°C of Peak Temperature (tP)	30 seconds
Maximum Ramp Rate	3°C/s
Preheat Temperature Range (Tsmin, Tsmax)	150°C–200°C
Preheat/Soak Time (ts)	90–120 seconds (120s maximum)
Liquidus Temperature of Solder (TL)	~217°C
Time Above Liquidus (tL)	60–150 seconds
Maximum Cool Ramp Rate	6°C/s
Maximum Device Surface Temperature	250°C

Wave Soldering

In wave soldering a conveyor moves the circuit board assembly over waves of molten solder causing joints between the solder pads and component leads. The following figure and table show SSO recommendations for a typical wave solder profile.

Figure 02: Pb-free double wave solder profile (not to scale). Temperature against time, with a preheat ramp, two closely spaced peaks at the first and second wave, and a cooling curve. The values are tabulated below.

Profile parameter	Value
Peak Wave Temperature	260°C
Maximum Time across Both Waves	10 seconds
Maximum Preheat Ramp Rate	4°C/s
Maximum Heat Ramp Rate	200°C/s
Maximum Cool Ramp Rate	5°C/s
Maximum Device Surface Temperature	250°C

Hand (Manual) Soldering

This is a manual process using a soldering iron. It requires a fairly high level of skill and dexterity, is time-intensive and is typically suited to prototype or short run builds.

If used, this soldering method comes with the following SSO recommendations:

Maximum Temperature: 350°C (at iron tip)
Maximum Time: 3s

SSO devices should undergo the manual solder process only a single time.