Method for correcting process temperature profile in a multi-zone thermal processor

• US 6,606,537 B1
• Filed: 04/19/2001
• Issued: 08/12/2003
• Est. Priority Date: 04/19/2001
• Status: Expired due to Fees

• Current Assignee: KIC Thermal Profiling, Co.
• Original Assignee: KIC Thermal Profiling, Co.
• Inventors: Kazmierowicz, Philip C., Moreau, Miles F.
• Primary Examiner(s): Picard, Leo
• Assistant Examiner(s): KOSOWSKI, ALEXANDER J
• Application Number:
  US09/839,325
• Time in Patent Office: 845 Days
• Field of Search: 700/121, 700/210, 700/207, 700/209, 700/299, 228/9, 219/497, 219/410, 219/388
• US Class Current: 700/210
• CPC Class Codes: G05D 23/1935 using sequential control

Abstract

A method for adjusting process temperature measurements used to monitor zone conditions in a reflow oven selects values for exclusion from correlation with the predicted part temperature profile. During the thermal process, a plurality of process temperatures over intervals may be measured along the reflow oven. Over a time period for the thermal process, a measured process temperature of this plurality may be evaluated for the maximum and minimum extremities, from which a difference for that interval may be calculated. This difference may be compared to a qualifier for the plurality, and be excluded from part temperature prediction if the difference for the interval exceeds the qualifier.

In an alternative embodiment, the maximum and/or minimum extremities from the plurality of process temperature measurements may be incorporated to produce a process temperature profile for correlation with the part temperature profile. The incorporation of measurement extremities may substitute for time-integrated measurement values otherwise used for attaining a target part temperature response.

Claims

1. A method for discriminating process temperature measurements used to predict a part temperature profile applied to a part in a thermal processor, said thermal processor having a correlation for predicting said part temperature profile, a plurality of zones and a plurality of temperature measuring devices disposed along said plurality of zones, said method comprising:

conveying the part into and out of the thermal processor through the plurality of zones for thermal processing within a time period;

measuring a process temperature during said time period by a temperature measuring device within the plurality of temperature measuring devices, said process temperature being aggregated to a plurality of process temperatures to form a process temperature profile;

calculating a difference between a maximum value and a minimum value within said process temperature profile;

comparing said difference to a qualifier value, assigning a logical value to a first value if said difference exceeds said qualifier value; and

disregarding said process temperature for inclusion in said process temperature profile by the corrector if said logical value equals said first value.

2. A method according to claim 1 wherein said plurality of temperature measuring devices are disposed on a probe installed in the thermal processor.

3. A method according to claim 1 wherein said qualifier value equals a characteristic statistical parameter multiplied by a first coefficient and adjusted by a second coefficient, said characteristic statistical parameter combining a plurality of differences calculated from said plurality of process temperatures.

4. A method according to claim 3 wherein said characteristic statistical parameter equals an average.

5. A method according to claim 3 wherein said characteristic statistical parameter equals a median.

6. A method for discriminating process temperature measurements used to predict a part temperature profile applied to a part in a thermal processor, said thermal processor having a correlation for predicting said part temperature profile, a plurality of zones and a plurality of temperature measuring devices disposed along said plurality of zones, said method comprising:

conveying the part into and out of the thermal processor through the plurality of zones for thermal processing within a time period;

measuring a process temperature during said time period by a temperature measuring device within the plurality of temperature measuring devices, said process temperature being aggregated to a plurality of process temperatures to form a process temperature profile;

determining a characteristic value to said process temperature, wherein said characteristic value is a function of a maximum value and a minimum value for said process temperature during said time period; and

assigning said characteristic value as a constant to replace said measured process temperature in said process temperature profile.

7. A method according to claim 6 wherein said plurality of temperature measuring devices are disposed on a probe installed in the thermal processor.

8. A method according to claim 6 wherein said characteristic value equals said maximum value.

9. A method according to claim 6 wherein said characteristic value equals said minimum value.

10. A method according to claim 6 wherein said characteristic value equals said maximum value multiplied by a third coefficient plus said minimum value multiplied by a fourth coefficient.

11. A method according to claim 10 wherein said third and fourth coefficients added together equal unity.

12. A method according to claim 11 wherein said third and fourth coefficients both exceed zero.

13. A programmable storage device readable by a machine tangibly embodying a program of instructions executable by the machine to perform method steps for discriminating process temperature measurements used to predict a part temperature profile applied to a part in a thermal processor, said thermal processor having a correlation for predicting said part temperature profile, a plurality of zones and a plurality of temperature measuring devices disposed along said plurality of zones, said method steps comprising:

conveying the part into and out of the thermal processor through the plurality of zones for thermal processing within a time period;

measuring a process temperature during said time period by a temperature measuring device within the plurality of temperature measuring devices, said process temperature being aggregated to a plurality of process temperatures to form a process temperature profile;

calculating a difference between a maximum value and a minimum value within said process temperature profile;

comparing said difference to a qualifier value, assigning a logical value to a first value if said difference exceeds said qualifier value; and

disregarding said process temperature profile by the correlation if said logical value equals said first value.

14. A programmable storage device according to claim 13 wherein said plurality of temperature measuring devices are disposed on a probe installed in the thermal processor.

15. A programmable storage device according to claim 13 wherein said qualifier value equals a characteristic statistical parameter multiplied by a first coefficient and adjusted by a second coefficient, said characteristic statistical parameter combining a plurality of differences calculated from said plurality of process temperatures.

16. A programmable storage device according to claim 15 wherein said characteristic statistical parameter equals an average.

17. A programmable storage device according to claim 15 wherein said characteristic statistical parameter equals a median.

18. A programmable storage device readable by a machine tangibly embodying a program of instructions executable by the machine to perform method steps for discriminating process temperature measurements used to predict a part temperature profile applied to a part in a thermal processor, said thermal processor having a correlation for predicting said part temperature profile, a plurality of zones and a plurality of temperature measuring devices disposed along said plurality of zones, said method steps comprising:

conveying the part into and out of the thermal processor through the plurality of zones for thermal processing within a time period;

measuring a process temperature during said time period by a temperature measuring device within the plurality of temperature measuring devices, said process temperature being aggregated to a plurality of process temperatures to form a process temperature profile;

determining a characteristic value to said process temperature, wherein said characteristic value is a function of a maximum value and a minimum value for said process temperature during said time period; and

assigning said characteristic value as a constant to replace said measured process temperature in said process temperature profile.

19. A programmable storage device according to claim 18 wherein said plurality of temperature measuring devices are disposed on a probe installed in the thermal processor.

20. A programmable storage device according to claim 18 wherein said characteristic value equals said maximum value.

21. A programmable storage device according to claim 18 wherein said characteristic value equals said minimum value.

22. A programmable storage device according to claim 18 wherein said characteristic value equals said maximum value multiplied by a third coefficient plus said minimum value multiplied by a fourth coefficient.

23. A programmable storage device according to claim 22 wherein said third and fourth coefficients added together equal unity.

24. A programmable storage device according to claim 23 wherein said third and fourth coefficients both exceed zero.

25. A device for discriminating process temperature measurements used to predict a part temperature profile applied to a part in a thermal processor, said thermal processor having a correlation for predicting said part temperature profile, a plurality of zones and a plurality of temperature measuring devices disposed along said plurality of zones, said device comprising:

a means for conveying the part into and out of the thermal processor through the plurality of zones for thermal processing within a time period;

a means for measuring a process temperature during said time period by a temperature measuring device within the plurality of temperature measuring devices, said process temperature being aggregated to a plurality of process temperatures to form a process temperature profile;

a means for calculating a difference between a maximum value and a minimum value within said process temperature profile;

a means for comparing said difference to a qualifier value, assigning a logical value to a first value if said difference exceeds said qualifier value; and

a means for disregarding said process temperature profile by the correlation if said logical value equals said first value.

26. A device according to claim 25 wherein said plurality of temperature measuring devices are disposed on a probe installed in the thermal processor.

27. A device according to claim 25 wherein said qualifier value equals a characteristic statistical parameter multiplied by a first coefficient and adjusted by a second coefficient, said characteristic statistical parameter combining a plurality of differences calculated from said plurality of process temperatures.

28. A device according to claim 27 wherein said characteristic statistical parameter equals an average.

29. A device according to claim 27 wherein said characteristic statistical parameter equals a median.

30. A device for discriminating process temperature measurements used to predict a part temperature profile applied to a part in a thermal processor, said thermal processor having a correlation for predicting said part temperature profile, a plurality of zones and a plurality of temperature measuring devices disposed along said plurality of zones, said method comprising:

a means for conveying the part into and out of the thermal processor through the plurality of zones for thermal processing within a time period;

a means for measuring a process temperature during said time period by a temperature measuring device within the plurality of temperature measuring devices, said process temperature being aggregated to a plurality of process temperatures to form a process temperature profile;

a means for determining a characteristic value to said process temperature, wherein said characteristic value is a function of a maximum value and a minimum value for said process temperature during said time period; and

a means for assigning said characteristic value as a constant to replace said measured process temperature in said process temperature profile.

31. A device according to claim 30 wherein said plurality of temperature measuring devices are disposed on a probe installed in the thermal processor.

32. A device according to claim 30 wherein said characteristic value equals said maximum value.

33. A device according to claim 30 wherein said characteristic value equals said minimum value.

34. A device according to claim 30 wherein said characteristic value equals said maximum value multiplied by a third coefficient plus said minimum value multiplied by a fourth coefficient.

35. A device according to claim 34 wherein said third and fourth coefficients added together equal unity.

36. A device according to claim 35 wherein said third and fourth coefficients both exceed zero.