tps model hs70 hot plate - university of texas at dallasrar011300/hotplate...note 1: the hot plate...

DOCUMENT TITLE: TPS Model HS70 Hot Plate Characterization of 19

DOCUMENT NUMBER: SP2013-LI-001 7/30/2013

AUTHOR: Roger Robbins

TPS Model HS70 Hot Plate

Operating Manual – and Performance Characterization Roger Robbins 7/30/2013

Clean Room Labs

The University of Texas at Dallas

Before you go and read the whole manual, here is how it works in manual mode:

1. Press “Power” button to turn it on or off.

2. Press “Heater” and arrow keys to set temperature.

3. Press “Enter” to accept value.

4. Hotplate will heat to temperature in 5 minutes and stay there.




TPS Model HS70 Hot Plate Roger Robbins 7/30/2013

Table of Contents TPS Model HS70 Hot Plate ....................................................................................................................... 1

Operating Manual – and Performance Characterization .......................................................................... 1

Table of Contents ................................................................................................................................ 2

TPS Model HS70 Hot Plate Characterization ............................................................................................ 4

Purpose ............................................................................................................................................... 4

Description .......................................................................................................................................... 4

Manual Operation ............................................................................................................................... 5

Details ............................................................................................................................................. 5

1. Manual Hotplate Bake .......................................................................................................... 5

2. Thermal Ramp-Up ................................................................................................................ 6

3. Thermal Ramp-Down............................................................................................................ 6

4. Timed Bake .......................................................................................................................... 6

Miscellaneous Operations ................................................................................................................ 7

Programed Operation .......................................................................................................................... 8

Rules for Programming .................................................................................................................... 8

Running a Program .......................................................................................................................... 8

Writing a Program ........................................................................................................................... 9

Characterization ................................................................................................................................ 10

1. Heating and Cooling Cycles..................................................................................................... 10

2. Programmed Cooling Curve .................................................................................................... 12

3. Programmed Heating Curve ................................................................................................... 13

4. Hotplate Surface Temperature Uniformity ............................................................................. 13

5. Vapor Extractor ...................................................................................................................... 15

Conclusion ......................................................................................................................................... 16

Appendix A - Specifications ................................................................................................................... 17

Torrey- Pines Scientific Hotplate Specifications – Model HS70.......................................................... 17




Appendix B - Example Heating Program ................................................................................................. 18

Soft-bake Heating Program for 100 um Film of SU-8 .......................................................................... 18

Purpose: ............................................................................................................................................ 18

Program ............................................................................................................................................ 18

Thermal Profile Results ...................................................................................................................... 19




TPS Model HS70 Hot Plate – Operating Manual Roger Robbins 7/33/2013

Purpose This document describes the operation and functional performance of the new Torrey Pines

Scientific (TPS) Model HS70 Digital Hot Plates installed in the table-top exhaust enclosures in Bay 2

(Lithography) of the UTD Clean Room Labs. The document is segmented into two sections: Operating

Manual and Characterization. Please read the Characterization section for a view of the hotplate

surface temperature uniformity – it will have an effect on where you place your samples.

Description The new digital hot plates are multifunctional and have a solid ceramic heater top which will

withstand aggressive chemical attack, however please do not test this aspect of the spec. The hotplate

will attain high temperatures, but the UTD Cleanroom recommended max is limited to 200 C in the

exhaust enclosure. The hotplate is designed for 1% temperature accuracy over the entire range (RT –

450 C) and will maintain a set temperature to +/- 1 C. (See complete specifications from the

manufacturer in Appendix A).

The LCD display shows three rows of information: temperature, stirrer speed, and timer value,

along with several icons indicating the mode of operation (Figure 2). The top number alternates

between the actual temperature (long display time) and the set point temperature (short display time).

The middle number shows the actual stirrer spin speed. And the lower row shows a time that counts

down to zero and in the manual mode turns off the hotplate (if desired) at time = zero.

The hotplate also is capable of following a programmed temperature profile designed by the

user. However there is considerable danger in running a program – if not written properly, the hotplate

has a propensity to run up to 450 C and stay there indefinitely. If you really want to write program,

please carefully read the instructions on programming and follow the rules exactly.




Manual Operation The operation of the Model HS70 hotplate is divided into Manual and Programed procedures.

All of the control buttons including the power ON/OFF switch are located on a membrane front panel as

shown in Figure 1. NOTE: Please do not drip Acetone on the front panel – it will melt it!

Figure 1. Operating panel for Programming showing the display and numbers.

Details

1. Manual Hotplate Bake – Standard manual hotplate operation.

a. Press the ‘Power” button to turn on the hotplate.

b. To set temperature of the plate, press “Heater”

c. Set the temperature by pressing the left-right arrow buttons to select the digit

to be changed and change the digit with the up-down arrow keys.

d. Then press “Enter” to accept the number.

e. Hotplate will start max ramp (450 deg. C per hour) to attain set temperature.

f. Note that the Temperature readout continuously toggles between “Target” and

“Actual” temperatures.

g. Temperature will stay at set temperature indefinitely in this mode of operation.




2. Thermal Ramp-Up – Increase the temperature at a predetermined rate.

a. Press the “Ramp” key and enter the desired ramp rate (deg. C per hour) using

the arrow keys

i. Press “Enter” to accept the number

ii. NOTE: Always enter the Ramp value before the temperature to create

the ramp action.

b. Then set the desired temperature

i. Press the “Heater” key and enter the temperature with the arrow keys.

ii. Press “Enter “to accept the number.

c. The hotplate will ramp at the desired rate until it reaches the set-point

temperature, and then remain at that temperature until it is instructed to

change.

3. Thermal Ramp-Down – Cool the sample at a predetermined rate (slower than its

natural cooling rate).

a. Press the “Ramp” button (at any temperature)

b. Then set the lower end-point temperature using the arrow keys.

i. Press “Enter” to accept the number.

ii. Note: Always enter the Ramp value before the temperature to create

the ramp action.

c. The hotplate will ramp at the desired rate until it reaches the new temperature

– it will stay at that temperature until it is instructed to change.

4. Timed Bake – heat a sample for a specified time and sound an alarm when complete.

a. TIMED BAKE: Bake a sample for a given time at some temperature and alarm.

i. Establish the desired temperature as in “Manual Hotplate Bake” above.

ii. Press “Time” and enter desired bake time using the arrow keys.

1. Put your sample on the hotplate.

2. Press “Enter” to accept the number and start the timer.

iii. The clock will immediately start timing and will “Beep” for 30 seconds at

the end of the time period.

iv. The temperature remains at the set point.

b. AUTO-OFF: Bake a sample for a set time and have the hotplate turn off and

alarm.

i. Establish the desired temperature as noted in step 1. – Manual Hot

Plate bake.

ii. Press the “Auto-Off” button – the word “Auto” will appear to the right

of the time value.

iii. Then press the “Time” button and tap the arrow keys to set the time.

1. Press “Enter” to accept the number and start the timer.




iv. The timer will count down, turn off the hotplate, and sound an alarm

when time runs out.

NOTE 1: The hot plate Red LED labeled “Plate Hot” flashes when the temperature

exceeds 50 C, warning users that the plate is “HOT.”

NOTE 2: If the temperature goes higher than 455 C, the red “Plate Hot” LED will flash,

sound an alarm, and turn off the heater for safety protection. However, when the

temperature drops below 450 C, the plate will turn back on again and continue to cycle

like this for an indefinite time.

Miscellaneous Operations

The hotplate heater can be turned off at any time by hitting the “Heater Off” button.

The stirrer can be shut off at any time by hitting the “Stirrer Off” button.

Entry mistakes can be erased by hitting the “Cancel’ button.

The hotplate itself can be turned off at any time by hitting the “Power” button.

The timer can be stopped by hitting the “Timer” button again.

The timer starts immediately after entering the time and hitting the “Enter” key.




Programed Operation

This hotplate has the capability to store ten programs of ten steps each which can be called and

run as desired. All programs will be open for change and must be examined before use to ensure that

the program operates as you need. There is a cycle step at the end of each program that enables the

program to repeat up to 98 times or indefinitely if the cycle number is set to 99. The program is set in

CMOS circuitry and will not be lost by power failure or turning off the heater.

To stop a program while it is running, press “Cancel”.

Rules for Programming

The timer can be used two ways in a program – with or without a ramp function. When the

timer is used with a ramp, the timer does not start to count down until the target temperature is

reached. When the timer is used without a ramp function, the timer starts to count down as soon as the

program starts. If you do not want a (slow) ramp in your program, but do want the timer to start when

the set-point temperature is established, you can use a ramp rate of 450 C/hr, which is usually faster

than the hotplate can respond anyway.

A Program step consists of a group of commands that include 1) Temperature, 2) Stirring Speed

(if wanted), 3) Ramp rate (if wanted), and 4) a timer setting. As you input a program, complete the

entries for all of these parameters before moving to the next step.

If a mistake is made while entering a program step, just hit “Cancel” on that step and make a

new entry.

To move to another program step, just hit the up or down arrow. The program number appears

rather inconspicuously just to the left side of the time. The time is indicated in the” hh:mm:ss” format.

After the last program step data has been entered, press “Enter” twice. The display will now

show “CYC 98” in place of the time value. This means the program will be recycled 98 times – press (and

hold) the down arrow until the number of cycles conforms to your desires (normally 01 cycle).

Running a Program

1. Press “RUN”. The display will show a flashing “ PROG 1” just to the left of the time value.

2. Select the program you want by pressing the up/down arrows until you find it.

3. Then hit “Enter”.

4. As the program runs, there will be a 5-beep alarm as the program starts each new step. And the

step number will advance just to the left of the Time indicator.

5. At conclusion of run, press “Cancel” to step out of programming mode for the next user.




Writing a Program

1. Press “Edit” to open the programming function.

2. Select the program number with the up/down arrow keys.

3. Hit “Enter” to activate the editing of this program.

4. Press the “Ramp” button and enter a value with the arrow keys if desired. Press “Enter” to

accept the new value.

5. Then Press the “Heater” button and enter a temperature (0 – 200 C) with the arrow keys, and

complete with the “Enter” key.

6. If a stirring operation is approved by Cleanroom Management, then you can enter the stirring

speed next. Press the “Stirrer” button and enter a stirring speed (50 – 1500 rpm) and then hit

“Enter” to accept the number.

7. Finally, set the time value for this step in hh:mm:ss format. Then hit the “Enter” button to

accept the time. This completes the program step.

8. Now move to the next step with the arrow “up” button.

9. Continue adding steps until your time and thermal profile is complete.

10. ENDING THE PROGRAM:

a. You MUST set a ramp rate for this event. It can be what you desire or just the max rate

of 450 C/hr for the natural cooling rate.

b. The temperature MUST be set to 0 C so the program will never achieve it and thus will

not bound up to 450 C at the conclusion of the program.

c. Clear the rest of the program steps to the end of the 10 step list.

11. Finalizing the program: Hit “Enter” twice at the conclusion of entering the last step. The time

value place will show a new value in the form of CYC 98 – meaning that the hotplate will repeat

(Cycle) the program 98 times in a row… Press (and hold) the down arrow key until you achieve

the number of program cycles you want. You probably just want 01 of them. Press “Enter”

again to select. This concludes the program generation procedure.

NOTE: Because of the propensity of this unit to thermally run away at the conclusion of

incorrect programming, I would encourage you to test the program to its end before running

your sample.

NOTE: See Appendix B for an example program designed for SU8 Soft Bake.




TPS Model HS70 Hot Plate – Characterization Roger Robbins 7/30/2013

Purpose The following discussion describes the initial operating characteristics of the new hotplates.

Parameters such as heating and cooling rates and controlled cooling characteristics as well as hotplate

temperature uniformity are measured and reported in the following sections.

1. Heating and Cooling Cycles

To characterize the hotplate performance, the first parameters to note are the heating and

cooling rates. We are setting a rule that these hotplates be used at temperatures no higher than 200 C.

So I collected temperature vs. time data between room temperature and the max 200 C. These curves

are shown in Figure 2.

Both the hotplates follow the same heating curve to a high precision. The time taken to reach

the set-point of 200 C is a little over 3 minutes, but stability is achieved only after another 10 minutes of

recovering from a 4 degree overshoot – which at 2% error may not be significant.

The natural cooling curve shows that in the current enclosure, the temperature will fall

exponentially to room temperature in about an hour. This is the maximum cooling rate and a

programmed cooling rate must therefore be less than this.

Note in Figure 2 that the heating rate is much faster than the cooling rate. This occurs because

the heating is controlled by a Proportional Integral Differential (PID) controller with 600 Watts of power.

The temperature is raised as fast as possible without too much overshoot or oscillation - (critical

dampening). The hotplate cannot demand a cooling rate faster than the natural cooling that follows

Newton’s law of cooling – “cooling rate is proportional to the temperature difference between the

starting temperature and the final temperature.” This results in an exponential cooling curve that

essentially represents the fastest rate of returning to room temperature after a heating event. If you

need a slower cooling rate, the hotplate can manage that in a linear fashion as slow as you desire.




Figure 2. Heating and cooling curve for the Torrey Pines Scientific (TPS) Model HS70 hotplates that sit

under the table-top Vapor Extractors in the UTD Clean Room Bay 2. This is an open-loop curve that

represents the quickest heating and cooling-change rates that the hotplate can achieve.

0

50

100

150

200

250

0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0

Tem

pe

rtu

re (C

)

Time (min)

TPS Model HS70 Hotplate Heating - Cooling Profile Open - Loop

7/23/2013




2. Programmed Cooling Curve

Figure 3 shows a sample cooling curve set by using the Cooling Ramp program mentioned in the

Thermal Down-Ramp section of the manual operation section above. This cooling curve was set for a

120 C per hour (or 2 C per min) cooling rate as an example. Shown in the same graph is the natural

maximum cooling rate. The cooling rate is nicely linear until it approaches room temperature where it

fades into the exponential shape of Figure 2.

Figure 3. Programmed and Natural (Free Cooling Rate) example for the TPS Hotplates.

0

50

100

150

200

250

0 20 40 60 80

Tem

per

atu

re (C

)

Cooling Time (min)

TPS Model HS70 Hotplate: Controlled DownRamp TH06 7/24/2013 RR

2 deg C/min Cooling Ramp

Free Cooling Rate




3. Programmed Heating Curve

The programmed heating (Example shown in Figure 4) curve is normally used to gently raise the

temperature of a sample to prevent such things as bubbling resulting from releasing internal solvent too

fast from a film. A slower temperature rise will allow solvent to migrate through the material and

escape through the surface without expanding into bubbles in the bulk of the film.

Figure 4. Example heating ramp compared to the maximum heating rate (with no ramp value set).

4. Hotplate Surface Temperature Uniformity

The uniformity of the temperature on the surface of the hotplate is a critical parameter which

helps determine how to utilize the hotplate. For example if you attempt to use one hotplate for an

array of samples, you might obtain a significant discrepancy in process performance between individual

samples due to unrealized temperature differences based on their position on the surface of the

hotplate. This uniformity measurement was made by setting the hotplate to a given temperature and

then measuring the surface temperature at selected locations with a surface thermocouple.

Measurements were taken on the diagonals and across the plate on bisector lines from left to right and

top to bottom. At high temperature, the uniformity is poor (75%) and at low temperature, the

uniformity is “better” (60%). Figures 5 and 6 show the measured results – note the astounding

temperature differences between the center and corner of the hotplate platen.

0

50

100

150

200

250

0 20 40 60 80 100 120 140 160 180 200

Tem

per

atu

re (C

)

Cooling Time (min)

TPS Hotplate: Controlled Heating Ramp 4/23/2009 RR

1 deg C/min Heating Ramp

Free Heating Rate




Therefore take note of this uniformity for multiple samples on the same plate - at least keep

them inside a circle of about 10 cm in diameter around the middle of the hotplate.

Figure 5. Temperature uniformity with a set temperature of 50 C along both x y axis lines as well as the

two diagonals.

Figure 6. Temperature uniformity with a set temperature of 200 C along both the x y axis lines as well as

the two diagonals.

0

10

20

30

40

50

60

-15 -10 -5 0 5 10 15

Tem

p (

C )

Distance (cm )

Static Lo-Temp Profile Over Hotplate Surface

Neg diag

Pos Diag

Y-Axis

X-Axis

0

50

100

150

200

250

-15 -10 -5 0 5 10 15

Tem

p (

C )

Distance (cm)

Static Hi-Temp Profile Over Hotplate Surface

Neg Slope diagonal

Y-Axis Temp

Pos Slope Diagonal

X-Axis Temp

7/24/2013




5. Vapor Extractor

The hotplate table top Vapor Extractor exhaust facility is designed to capture the solvent fumes

emitted while heating coated films to remove the remaining solvent before moving to the next

process step.

The concept of this design is to waft any vapor emitted from samples baked on these hotplates

into the exhaust away from users in the Cleanroom. The design is to have just enough airflow to

entrain the vapors in the exhaust flow but not to have so much airflow that the sample heating

uniformity would be affected.

In practice, there is no solvent odor noticed in the cleanroom during bakes using the Vapor

Extractor.

Figure 7. Vapor Extractor enclosure. Photo on left shows the hotplate inside the tabletop “Vapor

Extractor” fixture. This fixture is designed to extract fumes evolved from the sample out of the room

without creating a draft across the substrate which might cause film non-uniformity. The right hand

photo shows the lid up and the exhaust ports that suck air away from the sample via the lid.




Conclusion This document has briefly outlined the operation procedures, and characterized the hotplate

performance. Key results of the characterization are: 1) the hotplate is highly accurate in temperature

set point and ramp performance, 2) the heating table on the hotplate is ceramic and the temperature

uniformity is really poor – thus keep your samples at the center inside a 10 cm circle.

These hotplates are mounted inside a Vapor Extractor enclosure to capture any vapors emitted during

the bake.

NOTE: These hotplates have a propensity to thermally run away to 450 C if the programming is not

ended in the approved manner – read and understand how to end a program before doing inadvertent

damage to your samples or the to hotplate.




Appendix A - Specifications

Roger Robbins 7/30/2013

Torrey- Pines Scientific Hotplate Specifications – Model HS70

Programming:

Memory capacity 10 programs

Individual Program Capacity 10 steps

Repeat a program automatically 1 to 98 times or infinitely

Temperature Measurement:

Platinum RTD 100 ohm at zero in plate and in probe

Range 0–450°C

Readability 1°C

Hot Plate:

Dimensions 8” (20.3 cm) x 8” (20.3 cm)

Maximum plate temperature Ceramic 450°C

Temperature control type PID

Temperature accuracy 1% ±

Temp stability 1°C

Heater power in watts 600 watts

Stirrer:

Speed range unloaded 100–1500 rpm

Capacity 4 liters water

Readability 1 rpm

Settability nearest 10 rpm

Electrical:

115 VAC, 50/60 Hz, 600 watts

Fused both high and neutral lines

Line cord Detachable, 6 foot (1.8 meter), three-wire grounded




Appendix B - Example Heating Program

Soft-bake Heating Program for 100 um Film of SU-8 Using Torrey-Pines Hot Plate Model HS70

Roger Robbins 7/30/2013

Purpose: This appendix presents a sample thermal ramp program for a Soft-bake of a 100 um thick film of

SU-8 – 100 photoresist. The concept is to slowly ramp the temperature from room temperature to an

intermediate temperature to remove the concentrated solvent and then ramp to a higher temperature

for final removal of any solvent remaining in the film after coating. A final ramp back to room

temperature reduces the tendency for thermal forces to set stresses in the film.

Program Table A1

Example Program for the Torrey-Pines Hotplate, model HS70

Step # Parameters Setting Comment

Step 1 Heater = 65 C 1st stage temperature for heavy solvent removal

Ramp = 120 C/hr ~20 min ramp at 2 C/min

Stirrer = 0

Time = 00:10:00 10 minute bake at 65 C after ramp completes

Step 2 Heater = 95 C 2nd stage temp for final solvent removal

Ramp = 120 C/hr ~8 min ramp at 2 C/min

Stirrer = 0

Time = 00:30:00 30 min bake at 95 c at conclusion of ramp

Step 3 Heater = 0 C MUST set last step temp to 0 C using a ramp!!

Ramp = 240 C/hr ~24 minute cool-down – (4 C/min cool-down rate)

Stirrer = 0

Time = 00:00:00 Press “Cancel” at completion

Step 4 Heater = 0 Clear the unused steps

. Ramp = 0

. Stirrer = 0

. Time = 00:00:00

.

.

Step 10




Example: Thermal Profile Results The graph below is actual data produced by the hotplate by running the above program. Data

was collected from the LCD readout on the hotplate itself during the program run time. The “Timer”

profile represents the time indicated on the time line of the LCD readout during the thermal plateau

portions of the thermal profile.

Figure A1. Thermal profile data taken by running the example programmed above. Note the final ramp

rate cannot be sustained as the natural cooling rate catches up with the programmed value.

0

20

40

60

80

100

120

0 20 40 60 80 100 120

Tem

per

atu

re (C

)

Time (min)

TPS HotPlate Model HS70 SU-8 Soft Bake Profile

Count-down Timer Profile (min)

Thermal Profile

7/31/2013 RR

tps model hs70 hot plate - university of texas at dallasrar011300/hotplate...note 1: the hot plate...

Documents