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Technical Tips

Proper Furnace SetUp

Proper furnace setup is critical for successful high-yield Thick Film processing. The two key parameters that control successful firing are furnace air and the firing profile.

Furnace Air

  1. A sufficient quantity of clean, dry air must be present for thick film to fire correctly.
  2. Intake air should be drawn from a point 6 - 10 feet above the roof line and as far away as possible from contaminant-containing exhausts.
  3. Oil-free compressors should be used whenever possible.
  4. A series of dryers and filters must be used to dry to a dew point of -30°C at 80 - 100 psi. Standard cooling dryers in conjunction with heated desiccant dryers will achieve this value.
  5. Activated charcoal filters will help to remove halogen and sulfur-type contaminants.
  6. Micron and sub-micron filters will remove particulate matter.

To determine how much air is required in the furnace, use the following formula:

V = PLAWS where:
V = The volume of air in liters/minute required in the burnout section of the furance.
P = Printed area of the most dense circuit expressed as a decimal.
L= Belt load factor. How much of the burnout section is full when parts are loaded; expressed as a decimal.
A = Constant of 0.4 liters/cm2
W = Belt width(cm)
S = Belt speed (cm/min)

The amount of air required in the firing section is 10 to 20% higher than for the burnout section.

To set up the air flow properly:

  • turn off all flowmeters
  • turn up the burnout air to the value calculated above
  • turn the firing air to its value (1.1 to 1.2 times plaws)
  • check to make sure air is flowing out the entrance and exits of the furnace
  • turn up the venturi exhaust until room air is just being drawn into the furnace; this will ensure that all air introduced to the furnace is removed.
  • turn up the entrance and exit air curtains until flow at the exit and entrance is out of the furnace. This will prevent air from being drawn into the furnace.

Furnace Profile

There are several critical parameters that must be met in the furnace profile. Furnace profiles may be run with a traveling calibrated ungrounded Type-K or Type-N thermocouple. The Type-N is preferred because it shows less degradation with repeated use. The tables below list the critical parameters and the specifications associated with them.

Furnace Profile Specifications

60 Minute Profile
Control Point Nominal Tolerance Range
100C - 100C 55 min +/- 5 min 50 - 60 min
600C - 600C 31 min +/- 2 min 29 - 33 min
800C - 800C 19 min +/- 1 min 18 - 20 min
850C Dwell (Time) 10 min +/- 0.5 min 9.5 - 10.5 min
850C Dwell (Temp) 850C +/- 3C 847C - 853C
300C - 500C Ascent 45C/min +/- 10C/min 35C - 55C/min
800C - 600C Descent 30C/min +/- 5 min 27C - 33C/min
700C - 300C Descent 50C/min +/- 10C/min 40C - 60C/min
Burnout Removal 500C +/- 50C 450C - 550C

30 Minute Profile
Control Point Nominal Tolerance Range
100C - 100C 33 min +/- 3 min 30 - 36 min
600C - 600C 19 min +/- 1 min 18 - 20 min
800C - 800C 14 min +/- 1 min 13 - 15 min
850C Dwell (Time) 10 min +/- 0.5 min 9.5 - 10.5 min
850C Dwell (Temp) 850C +/- 3C 847C - 853C
300C - 500C Ascent 95C/min +/- 10C/min 85C - 105C/min
800C - 600C Descent 70C/min +/- 10C/min 607C - 80C/min
700C - 300C Descent 95C/min +/- 10C/min 80C - 105C/min
Burnout Removal 500C +/- 50C 450C - 550C