Lab Week 7: Pin-In-Paste Calculations, Deposition and Reflow Soldering

EET360

Lab Week 7: Pin-in-Paste Calculations, Deposition and Reflow Soldering

The labs will be divided in half, with the first 8 people coming at the lab start time, and the second 8 people coming 50 minutes later. I.e., if you have a 3:30 lab, the first 8 come at 3:30, the second 8 come at 4:20.

Object: this week in lab, working in pairs, you will:  Determine and verify the amount of solder paste necessary to obtain good solder joints using the pin-in-paste method with through-hole parts.  Apply that amount of paste into and over the appropriate through-holes  Insert parts into through-hole paste,  Reflow the assembly on the Zevatech 415 reflow oven in Knoy 258  Inspect and critique the solder joints that result

Tools:  Time-pressure paste dispensing system  Acculab analytical balance  Z415 Reflow oven

After the prelabs are checked, one lab group will be assigned to startup the Zevatech 415 oven in Knoy258. All groups will reflow their PIP boards in the oven in Knoy258.

Prelab 15 points, must be completed prior to lab: Instructor’s prelab grade = _____ The PCB you will use is 0.0625” thick and has a series of holes 0.037” in diameter. You will insert ICs that have leads that are 0.010” X 0.021”. Show the equations you use and the resulting calculations to find: 1. Volume of one hole =

2. Volume of one lead wholly within one hole =

3. Δ volume = volume of required metal =

4. Multiply Δ volume by 125% for fillet formation =

5. Volume multiplier for syringe-deposited paste =

6. #4 X #5 = volume of syringe-deposited paste required =

7. Percent of #6 that will fit in a filled board hole =

8. Percent of the required paste volume that must be in excess of hole fill = Procedures:

Paste deposition: 1. Obtain a test board from your instructor. Identify the appropriate SIP or DIP holes for solder paste fill. 2. Clean the board with alcohol, holding the board with gloved hands. 3. Weigh your board on the balance, and record the initial weight. 4. Using the time-pressure dispensers at 35 psi, determine the dispense time that will result in a visual 100% hole fill. (You may need to use the vacuum pull-back feature on the dispenser.) Your team should agree on the 100% hole fill volume. Clean all deposits from the board. 5. Continuing to hold the board with gloved hands, create 10 deposits using the agreed-upon dispense time. 6. Reweigh the board. Based on a density of 138 gm/in3, determine the actual volume of your “100% hole fill” volume. Record this as “control volume”. 7. Add to the timing of your dispenser the % over 100% hole fill you calculated in prelab to result in the actual volume of syringe-deposited paste required. This will give you the complete volume you have calculated in the prelab as necessary to create a good solder fillet. 8. Make a sketch of the board with the hole pattern you will be using clearly shown, along with one or two nearby board features – for identification purposes. 9. Deposit paste into 6 holes of the board you will reflow using that time setting. Mark the location of these 6 holes on your sketch. 10. In three other holes (holes 7-9), increase the time setting by 50% and deposit that portion at those three holes. Record this setting as the “overfill” setting, and mark on your sketch which three holes had this amount of paste. 11. In yet three other holes (holes 10-12), decrease the time setting by 50% from the original setting – not from the setting in #11- and deposit that amount of paste. Record this setting as “underfill”, and mark on your sketch which three holes had this amount of paste. 12. Carefully insert appropriate through-hole part(s) into the holes. Paste will be pushed through the holes, so be careful not to touch anything to the bottom of the board. The components must be pushed all the way into the board, so that the bottom of the header sits on the board.

Reflow: 13. Take the board to Knoy 258, set the board into the reflow oven, supporting the board off the conveyor with spacers. 14. Observe the reflow sequence. 15. When the reflow sequence is done, allow the board to cool. Then examine the solder fillets for acceptable volumes, using the IPC book as a guide. Record your findings and your analysis of which fillets, if any, are acceptable. NOTE that a fillet which touches the bottom of the component body is not acceptable because it is too large. 16. Take pictures that will demonstrate your acceptable, too much and too little fillets. Do not take the board from lab.

Report: Not a formal report. For this week include:  A cover sheet  all information you have been asked to Calculate or Record, including your Prelab work,  the results of anything you have been asked to inspect or examine, including pix, and  a complete description of the procedures that resulted in your finished solder joints.