Reflow Oven Guidelines

⚠️Training Zone Ahead⚠️

To safely use the following equipment, you must receive training by lab64 Staff prior to individual use. To get trained, please attend one of our Office Hours sessions↗. Estimated Length of Training: 15 minutes.

Introduction

The Reflow Oven

The retrofitted Black and Decker toaster ovens make for decent reflow ovens, once an additional heating element and insulation have been added! It is a quick way to solder populated boards. Our three units are located on the side counter of Packard 129, and are affectionately named Bubba, Ian, and Susan

Preparing To Reflow

1.

First, prepare your PCB for use. Make a jig of the approprate size for your PCB using copper clad laminate (CCL) and blue painters tape as shown in the adjacent photo.

2.

Place your board in the jig. Ensure that it fits snugly with no wiggling

3.

Align your stencil so that the holes perfectly overlay on top of the pads. Tape the stencil in place aong one side using painters tape.

4.

Next, prepare the solder paste. If you don’t see it on the counter, come find Jeff and he will provide you some paste. We often keep it tucked away because students often inadvertently leave the lid off when done, and doing so will dry out and ruin an entire jar of expensive paste in the blink of an eye! Using a wooden dowel, apply a small layer of paste to a putty knife along the entire tip’s edge.

5.

With a pressing and sliding motion, spread the solder over the holes in the stencil by holding the putty knife at the angle shown in the clip.

6.

Carefully lift the board out of the jig—make sure you don’t inadvertently smudge any of the paste that has been placed on the pads.

⚠️

If you are done pasting your board(s), it is time to clean up! Return any excess paste into the jar. IMPORTANT: Make sure you close the lid of the solder paste. Failure to do so will ruin the paste.

You can use isopropyl alcohol (IPA) to clean up the putty knife, wooden stick, counter and stencil (a small brush can found near the solder paste to help get in the holes of the stencil). Place any paper towels into the plastic container marked Solder Paste.

7.

Take your parts and begin to populate your board. Use of the microscope in the rework room may assist you if your eyes are not up to the challenge. It is a delicate operation, using tweezers to gently place the component on top of the solder paste without smearing the paste around. A VERY GENTLE tap on the component can help to seat it a little bit to prevent it from sliding off during transport or reflow. Don’t press so hard that the paste squooshes out beneath the component.

Using The Oven

1.

Place the board between halfway and two-thirds of the way back into the oven (the front edge does not get reliably as hot as we want). Leave the sheet of foil on the tray in place, it helps with the heat transfer.

2.

Close the lid, and from the front panel you can select the profile you want. Unless you have a special custom solder paste or application, you will want to select profile 1, a lead-free paste profile that reaches 250 degrees C at its peak temperature. Then, select Run Profile.

3.

After about 5-6 minutes, the door will open slightly to begin the cooling process. Once the temperature gets below 100 degrees, you will hear an audible signal that indicates the reflowing process is complete, and being careful not to burn yourself, you can remove the part.

⚠️

Note: If you are doing double sided boards, please begin by populating and reflowing the side with lighter components as these will tend to stay in place (surface tension) when flipped upside down to reflow the other side. In this instance, you will want some metal standoffs, thick hex bolts, etc. to get the board off the tray so the bottom components are not touching the tray.

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