Start Your Furnace Project with 6 Questions

The photo below shows the control panel of a customized furnace. It is for our customer doing metal annealing process in Europe. Like many customized equipment, there are a lot of details to consider when it comes to the entire design of a belt furnace system. The following 6 questions are good ones to start with.

1)What is the application?

Some common applications are thick film firing/drying, paste drying, glass to metal sealing, solar cell processing, soldering, brazing, sintering, annealing, curing.

2)What is the product material, dimension, weight? What carrier do you use to hold the products in the furnace?

This will help decide the belt loading capacity, chamber dimension, driving power, how easy it can be heated or cooled.

3)What is the desired productivity?

This will help the design of furnace length, belt width, belt speed.

4)What is the time-temperature profile?

This will help design the heating zones, cooling method(air cooling or water cooling).

5)What is the atmosphere requirement?

Common atmospheres are air, N2, Ar, H2, O2.

6)What is the footprint limit(max length/width of the furnace)?

This will ensure the furnace can fit the facility.

The root of a perfect design lies in the good communications between designers and end users.

------Torrey Hills Tech Furnace Team

Welcome communicate with us!

http://www.beltfurnaces.com/


Contact: Sean Song

song@torreyhillstech.com

Do I need a belt furnace for BBQ?--3 Reasons Not to Use a Belt Furnace

The yummy picture was taken last Friday. My colleagues and I cooked BBQ lunch together. Though we deal with belt furnace everyday, we used two batch ovens. Our reason is a belt furnace does not have a sauce dispenser inside!

Unlike BBQ, more and more manufactures are changing from batch production to continuous production. In furnace application industry, this corresponds to changing from batch furnaces to belt furnaces. Though this is the trend, there are reasons not to do so.

1. A belt furnace is expensive

Good point. But you can increase productivity and save labor cost by implementing continuous production.

2. A belt furnace takes up much space

That is true. Some big belt furnace can be over 100ft long. Not every facility can hold such a long tool. One can use multiple shorter furnaces instead of a big one---each furnace runs at lower belt speed and smaller productivity, but adding up contributions of each furnace will get the expected productivity. Multiple smaller furnaces also improves redundancy—even one of the furnaces needs maintenance, other furnaces can keep the production going on.

3. My product is so heavy that the belt loading capacity is exceeded.

Very practical question. Though we can use reinforced belt with loading capacity over 25 lb/ft2, some products are much heavier. Pusher kiln may be a good option for continues production for super heavy products.

What is your reason to say "Yes" or "No" to continuous production in heat treatment process? How do you like the idea of a BBQ belt furnace?

Interested in a belt furnace, see more at http://www.beltfurnaces.com/

More Hydrogen, Less Oxidization?

One of our atmosphere furnace users recently consulted us regarding the surface brightness of the SS products. The user found the SS product surface had oxidization and then increased H2 flow rate expecting to solve the oxidization, but turned out the oxidization issue was not getting better. It is a little confusing. “More H2, less oxidization”, should not it be true?

H2 is a common reducing atmosphere. It has been used in applications like annealing, brazing and etc. According to our experience, H2 plays an important role in achieving bright surface finish for metals like SS, silver and etc. In brazing, H2 has the effect to improve the wettability by removing the oxidization surface of the melting filler material.

However, it is not always true that more H2 equals less oxidization. Here is why.

•  H2 source can contain impurities like water, oxygen.
•   H2 can react with oxidizations on the metal belt surface and produce H2O. Then the H2O can react with the SS product in the furnace, causing SS oxidization. In this case, H2 acts like a carrier that transfer the oxygen element from metal belt oxidization layer to the SS product.

Knowing why more H2 may not be beneficial, what can we do to eliminate product oxidization? Here is our suggestions.

• Choose high purity gas. Dew point of the gas needs to be below -50C for SS bright surface finish. When necessary, use gas purifier before connecting the gas to the furnace
• Adjust flow rate of N2 to help lower down the O2 level in the furnace chamber. For gas cost and safety concerns, it is recommended to choose N2 as the major gas to control O2 level.
•   Maintain clean operation of the furnace belt. Using in-line ultrasonic belt cleaner is a good option. 

After several trials, our furnace user was happy to get the bright surface finish.

Have you encountered oxidization issues when using a belt furnace? How do you solve it? Welcome sharing your ideas with me  song@torreyhillstech.com

More about furnaces please check http://www.beltfurnaces.com/

Influence of belt furnace on engine valve heat treatment

http://www.beltfurnaces.com/doc/Engine_Valve_white_paper.pdf

Influence of belt furnace on engine valve heat treatment

What is an engine valve?
Fig 1 shows typical engine valves. Engine valves are essential parts for engine functioning. They
are located in the cylinder head and can be classified into intake valves and exhaust valves. The
intake valves bring in air/fuel into chamber for combustion and the exhaust valves let exhaust
out after burning. The open and close of valves are decided by the cylinder piston positions. A
detailed explanation by Marshall Brain on how engine works can be found at
http://auto.howstuffworks.com/engine4.htm.

Fig 1. Typical engine valves (Courtesy of online picture http://www.plxsport.com/atv-partsvalvetrain-wiseco-titanium-intake-valve-suzuki-ltr-450?att_id=0)
Engine valves heat treatment description
The working conditions of engine valves are severe. Doug Kaufman states that intake valves
typically run at the range of 800F—1000F (427C-538C) while exhaust valves typically run at
1200F—1450F (649C-788C), due to the temperature difference of intake gas and exhaust.
Besides high temperature, valve also experiences cyclic loading. A valve can open and close
dozens of times per second.
Because of the high working temperature and strength required in such conditions, heat
resistant steels are often used. Besides proper material selection, proper heat treatment is
essential in manufacturing high performance engine valves. It is vital to create the desired
properties like strength, wear resistance, toughness, fatigue strength, hardness and
microstructure.
Normal heat treating methods include annealing, normalizing, tempering and hardening. To
decide a specific heat treatment process, alloy phase diagram (Fig. 2) is the fundamental tool.

Fig 2.Fe-C phase diagram (Courtesy of online source http://www.calphad.com/iron-carbon.html)
A typical heat treating process for VAZ PASSENGER CARS engine valves was published in.
Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 6- 9, 1996. Several major
steps in the heat treatment process for inlet valves includes:
1)  Preliminary heat treatment, annealing to around 700C for 3—4 hours to obtain
Spheroidized pearlite with certain hardness.
2)  Stabilizing annealing.  Hold 2-3 hours at 600 - 620°C to release stress and eliminate
warping issues that might occurred in other process
For outlet valves the heat treatment process is a little different because of the quality
requirement difference between inlet and outlet valves.
HSK fast firing furnace for engine valve heat treatment
The HSK series fast fire furnace heats from ambient to 1050C in approximately 40 minutes and is
designed to sustain continuous on/off heating and cooling cycles resulting from alternating
periods of production and non-use. It features an ultra-clean low-mass refractory heating
chamber equipped with FEC (Fully Enclosed Coil) heaters formed into ceramic insulation panels.

With the use of advanced insulation materials, lower thermal capacity enables the furnace to
warm up and cool down very quickly and lose less heat to the environment.
To prevent valves from falling off the belt, a hearth plate with walls can be incorporated within the
furnace. The belt would travel through the furnace on a metal hearth plate with side walls, which would
prevent products from falling off the belt.
Appendix I shows the brief technical details of a HSK fast firing furnace.

APPENDIX I
Technical Specification for Model HSK Series Conveyor Furnace
Main Characteristics
Specification  HSK2505-0611
Rated Temperature  1,050 deg. C
Belt Width   250mm/10"
Above Belt Clearance  50mm/2.0"

Specification  HSK2505-0611
Heating Length  2700 mm/106.3"
Cooling Length  1240 mm/48.8"
Control Zones  6
Conveyor Speed  30-200mm(1.2"-8")/min
Overall System Width   1200 mm/47.2"
Overall System Length   6905 mm/272"
Overall System Height   1350mm/53"
Typical Temp. Uniformity  +/-3 deg. C
Net Weight   1,200kg
Power
AC 220-480V, 3 phase, 5 wire, 50/60 Hz, 42 kW
Power draw at normal operating conditions: <15kw p="">
References
[1]. Kiyoshi FUNATANI. HEAT TREATMENT OF AUTOMOTIVE COMPONENTS: CURRENT
STATUS AND FUTURE TRENDS. Trans. Indian Inst. Met.Vol.57, No. 4, August 2004, pp.
381-396
[2]. Doug Kaufman. Understanding Valve Design and Alloys
[3]. IIT BOMBAY. Design for heat treatment, online presentation
[4].  A. N. Cherdantsev, A. N. Makar'ev, V. P. Akhant'ev, I. N. Kaplina. Technology for heat
treatment of engine valves of VAZ passenger cars. Metallovedenie i Termicheskaya
Obrabotka Metallov, No. 10, pp. 6- 9, 1996.

A wonderful Battery show

 Big truck at the show place

 Our belt furnace booth E1247

 Furnace Guy with happy customers

 Electric motorbike

Thanks Soulbrain for the nice poster

Please contact song@torreyhillstech.com for any furnace related questions.

http://www.beltfurnaces.com/

Questions for furnace? We have the answers!

1) How can we conduct a gas/energy consumption analysis and optimize the gas/energy usage for a muffle furnace?

To protect the muffle, a muffle furnace usually stays powered on at all times.

Gas consumption depends on the furnace sides, as well as the oxygen content requirement. When the furnace is not working with a load (during night shift, for example) the gas flow can usually be turned down to 30% - 40% of the working rate.

With an optimized structure and superior insulation design, our furnace is energy efficient. After reaching the required profile, the heating elements will work at about 50% or less of the maximum power output. This extends the lifespan of heating elements, and saves power. When the furnace is not working with a load, the insulation power of empty furnace is usually 20% - 35% of the max power output.

2) What are common spare parts that a customer should stock to guarantee uninterrupted operation of a belt furnace? How often are these parts replaced?

Typical spare parts include a belt, a brush, a Solid State Relay, a cooling fan, a thermal couple, heating elements, et cetera. Under normal working condition, our furnaces can run 3-4 years without needing any major parts replaced.

3) What does a customer need to do to prepare for a belt furnace installation?

The following elements must be ready before the belt furnace can be installed:

• - Power Supply
• - Gas Supply
• - Exhaust System
• - Water Cooling System

Our engineers will issue clear instructions on this preparation beforehand.

4) Is there a device that can be installed in a belt furnace to prevent parts from falling off of the belt?

Yes. A hearth plate with walls can be incorporated within the furnace. The belt would travel through the furnace on a metal hearth plate with side walls, which would prevent products from falling off the belt.

5) What types of control systems will work with the belt furnace’s operation system?

- Direct controllers on the furnace will offer basic control of parameters, such as zone temperature, belt speed, et cetera.

- A Windows-based industrial computer control system allows for easy profile setting, storage of multiple profiles, an straightforward working status monitor, and easy access to all operating data history.

- Beckhoff embedded control systems are suitable for customers that require a Beckhoff embedded control system.

6) What is the most common type of gas used to form a gas curtain in the furnace?

Nitrogen is most commonly used for a gas curtain. It is inert, safe, and effective in keeping air out of the furnace. Additionally, the cost is relatively low.

7) What is a FEC heater?

FEC stands for Fully Enclosed Coil, which means that the heating wires are embedded within the ceramic fiber boards. This design protects the heating wires, and also provides power distribution evenly in order to maintain the temperature uniformity.

8) What is a commonly used insulation material in a furnace?

Alumina silicate fiber is a high performance insulation material commonly used in our furnaces. It has small density, as well as good energy saving performance.

9) What are the requirements for a cooling water system?

Usually, the cooling water needs to meet requirements for pressure. Also, a proper corrosion inhibitor must be added.

Still have a question? Ask song@torreyhillstech.com

http://www.beltfurnaces.com/faq.html

Torrey Hills Tech will join Battery Show with its furnace systems for Li battery manufacturing

Taking place September 16-18 2014, in Novi, Detroit, Michigan, The Battery Show 2014 is the premier showcase of the latest advanced battery technology. 

Torrey Hills Technologies(http://www.beltfurnaces.com/index.html) will be introducing its belt furnace systems for battery manufacturing to all the exhibitors. Li ion battery manufacturing requires Ar/N2/H2 protective atmosphere at relatively high temperature.

Torrey Hills Tech HSA series furnaces are the best choice for Li ion battery manufacturing.

The HSA series furnace is an efficient furnace designed and used for heat treatment 

for processes such as LiFePO4. It features a low mass refractory heating chamber equipped 

with ceramic FEC (Fully Enclosed Coil) heating board. The HSA furnace has 6 independent 

zones able to reach 1150˚C, temperatures high enough to heat treat lithium iron phosphate. 

The temperature profiles are able to run at the desired heating rate to meet the required 

sintering temperatures under controlled atmosphere. Gas is independently controlled for the 

adjustment of air, nitrogen, hydrogen, and argon inflow. Temperature control zones allow the 

furnace to run at the proper heating rate to meet the needs for firing and curing. The 

conveyor system allows proper heating across the belt with little temperature variations. The 

furnace is monitored by type K thermocouples with each zone monitored by single loop PID 

temperature controllers. This enables precise and stable temperature control throughout the 

heating process to the cool down. 

The furnace is large enough to handle manufacturing processes for LiFePO4

applications. It has a 14” (35cm) belt width and a 130” (330cm) heated length. The conveyor 

system can run at speeds of 1-8 Inches/min. The HSA furnace is protected from 

overheating, over loading, and low gas pressures. It also comes equipped with anti shock 

protection on the doors during maintenance. Technical information and training will be given 

upon installation of the furnace to ensure proper practice for continued use. Emergency 

buttons and removable collection traps are also located on each end of the furnace. For the 

cleaning system, there is a rotating motor metal brush that cleans the belt so future products 

will not be contaminated.

Have any question? Contact song@torreyhillstech.com

Torrey Hills Technologies Hengli brand furnace win silver award!

(SAN DIEGO, CA, Aug. 5, 2014)   – Torrey Hills Technologies, LLC (THT) and Hengli Eletek, Co. Ltd  were jointly named as a Silver winner in Most Innovative Product of the Year in the Enterprise category of Best in Biz Awards 2014 International, for inventing a volatile organic compound (VOC) removal / thermal oxidizing system. Best in Biz Awards are the only independent business awards program judged by members of the press and industry analysts. Other winners of this prestigious award include Toshiba, Dell, BlackBerry, Epson, Lenovo, and more. For a full list of gold, silver and bronze winners in Best in Biz Awards 2014 International, visit: http://intl.bestinbizawards.com/intl-2014-winners.

 

Concerned about the negative impacts of modern manufacturing on environment, the Hengli/THT team designed a ground-breaking VOC removal system for their model AST belt furnace. Connected to the furnace exhaust, the VOC removal system eliminates VOC emissions before reaching outside air. Widely used in electronics manufacturing as solvents that are dried on a belt dryer and exhausted into the air, VOCs are one of the top causes for smog. The electronics manufacturing process contributes a significant portion of VOCs to air pollution, yet THT and Hengli are the first to achieve a green solution that allows VOCs to be oxidized into CO2 before being released into the ambient air.

“It was a pleasure to collaborate with Hengli on this important solution," said Ken Kuang, President and CEO of THT. “We are honored to be named as Silver winner for the 2014 Best in Biz Awards, and we are confident about the positive impact of this technology on environment.”

Torrey Hills Technologies, LLC ( http://www.torreyhillstech.com , http://www.beltfurnaces.com ) is a leader in developing and delivering quality yet affordable equipment and supplies for multiple industries. Since its establishment, the company has expanded its business from microelectronics packaging components to large-scale furnace equipment for semiconductor packaging, circuit board assembly, advanced materials processing and solar cell manufacturing. Headquartered in San Diego, Calif., the company now has customers located around the world in North America, South America, Europe, Asia, and Australia.

Hengli Eletek Co., Ltd. was founded in 1992 with the mission to become a leading supplier of thermal processing solutions to the global electronics and materials markets. Hengli products have been highly appreciated by customers from more than 20 countries located in North America, South America, Europe, Asia, and Australia.

Best in Biz Awards recognizes top companies, teams, executives and products for their business success as judged by established members of the press and industry analysts. Best in Biz Awards honors are conferred in three separate programs: North America, EMEA, and International. For more information, please visit the official web site: http://www.bestinbizawards.com.

Ultrasonic Belt Cleaner/Cleaning for Belt Furnaces - A Presentation

An ultrasonic belt cleaner utilizes ultrasound technology with transducers, which are positioned in the cleaning tank. These transducers emit sound waves in a purifying solvent, which thoroughly scours the belt on conveyor belt furnaces. Compared to metal brush cleaning, this method cleans the belt faster, with more precision and consistency. For more information, please visit www.beltfurnaces.com.

Influences of Belt Furnace on Post Mold Cure Process

Please contact song@torreyhillstech.com for any question on belt furnace.

Introduction

      Post mold cure (PMC) is one of the most significant processes in electrical industry. This process exposes part of a mold to elevated temperatures in order to speed up the curing process and to optimize some physical properties of the material.

      The PMC process will expedite the cross-linking process and properly align the polymer's molecules to make a stronger part with better high temperature characteristics. Much like tempering steel, post curing thermosetting can improve physical properties above what the material would normally achieve at room temperature, such as tensile strength, flexural strength, and can modify the temperature of heat distortion. Moreover, post mold cure process is the most common strategy used today for warpage problem solution. Finally, it can also deal with the outgassing phenomenon during IC package.

      Given the benefits of PMC processing, it is widely used in the electrical device industry. It is easy to find the application of PMC in many facilities and there are a large number of companies using PMC on their products. Figure 1 shows various chips that have been packaged using PMC processes.

Fig.1 Products of PMC

PMC Process in IC Encapsulation

      There are two major manufacturing steps in IC encapsulation industry. For the first step, the IC chip would be encapsulated into a thermosetting epoxy mold compound (EMC), which is the most common plastic material for IC package manufacture today. This pelletized compound is injected into a hot mold die to form the body around the IC die. And after the plastic injection, the mold is cured. The object of this step is to achieve good fill and partial cure of the mold.

  The second step of the process is the post mold cure (PMC) process. The goal of this step is to increase degree of cure and reduce warpage in an IC chip. In order to optimize properties, the PMC process provides a critical completion of the cure process to complete the chemical cross-linking of the material. During PMC, the material experiences additional molecular rearrangement and greater efficiency of molecular collisions resulting in a greater degree of cross linking. The heating can also cause any residual peroxide to break apart and initiate some additional chains.

  Generally, a PMC heating process can be divided into three heating stages, assuming that heating process in the furnace is uniform. In the first stage, products are heated from room temperature 25 ^oC to post mold cure temperature 175 ^oC in a short time. In the second stage, the temperature is held constant for several hours. In the final stage, the product is cooled from 175 ^oC to room temperature in a short interval.

Applications of PMC

      Post mold cure has been applied by many electronics companies, especially semiconductor designers and manufacturers. Table 1 shows various products that have benefited from PMC to achieve better performance as well as some companies associated with them. From the table, it is easy to see PMC technique is widely used in electronic market by a wide range of corporations. If your company requires better device performance, PMC processing is an easy choice.

Table1. Some products and companies using PMC process

Products	Companies
IC	Intel; Samsung; Toshiba; SK Hynix; IBM; Sony; AMD; Freescale; Marvell; Nvidia; Qualcomm; Anadigics; Cree; Infineon; ST’s; Microsemi; Silicon Labs; TI; Vishay; IR; NXP; Intersil; Amkor; Spansion; Renesas;
Packaging	ASE; Intel; TSMC; Microsemi; SPIL; QuickLogic; SMIC; UMC; Globalfoundries; Amkor; UTAC;
RF power amplifier	Skyworks; TI; TriQuint; RFMD;  Cree; Anadigics; Maxim Integrated; Infineon; NXP; ST’s; Avago; Semtech; ADI; Linear; Macom; Freescale; Microsemi; ONsemi; Lattice;
Memory	Samsung; Elpida; ISSI; Micron; Maxim; Integrated; Microsemi; SK hynix; NEC; Panasonic; Toshiba; SPIL; OSE; Spansion; Winbond;
FPGA	Xilinx; Altera; Atmel; Microsemi; Lattice; QuickLogic; Actel; Vantls; Cypress;
ASIC	LSI Logic; Toshiba;
Attenuators	Skyworks; TriQuint; RFMD; Avago; Peregrine; Analog;
RF passive	Skyworks; TriQuint; RFMD; PPI; Macom; Microsemi; ONsemi; RCD;
Transistor	TriQuint; NXP; ST’s; Avago; ONsemi;
Diodes	Skyworks; NXP; ST’s; Avago; Macom; Microsemi; Vishay; ONsemi;
Mixers/ multipliers	Skyworks; TriQuint; RFMD;NXP; Avago; ADI; Linear; Peregrine; TI; Vishay; Analog;
Filters	Skyworks; TriQuint; Avago; Macom; TI; ONsemi;
Modulator/ demodulator	Skyworks; TriQuint; RFMD; NXP; ST’s; Micron; Avago; Linear; Microsemi; Analog;
Switches	Skyworks; RFMD; Infineon;  NXP; Maxim Integrated; ST’s; Avago;  ADI; Macom; Peregrine; Microsemi; TI; Vishay; ONsemi; Analog;
Die/wafer	TSMC; TI; Fairchild; Vishay; IR; Cypress; SPIL; SMIC; Amkor;

Influences of PMC on Material Properties

      It is the epoxy molding compound (EMC) that determines the properties resulting from PMC process. Epoxy is the vital part of EMC. It will directly affect the flow characteristics of EMC as well as impact the EMC thermal performances and electrical characteristics. Table 2 shows some commonly used epoxy resins and their characteristics.

Table 2. Some epoxy resins and their characteristics

Epoxy resin	Characteristics
O-cresol-type epoxy resin	High thermal stability and chemical stability
Bisphenol A type epoxy resin	Low shrinkage and low-volatile component
Multi-functional-type epoxy resin	Excellent thermal stability, fast curing and high Tg
Biphenyl-type epoxy resin	Low viscosity, high filling
Tea-type epoxy resin	High Tg, high-heat-resistant
Modified epoxy resin	Good flexibility

     A PMC process involves placing the molded articles in a forced-air furnace and thermally treating them to a series of increasing temperatures for various times. The program of times and temperatures is referred to as the cure schedule or cure cycle. During the PMC process, the molecular weight of the polymer increases by chain extension. And as the molecular weight increases virtually all mechanical, chemical, and thermal properties are changed. Figure 2 illustrates how physical properties change during a PMC process. After PMC, the physical properties of objects are substantially increased.

 

Fig.2 Physical properties changes of cure circle: (a) Tensile strength; (b) Flexural strength; (c) Heat deflection Temperature; (d) Shrinkage; The specimens are Torlon 4203L, 3 mm (1/8 inch) thick.

      PMC can prevent problems such as warpage during encapsulation in chip packages. In IC encapsulation, one of a prevalent and troublesome EMC defect is warpage. Fortunately, PMC is an efficient method to alleviate the warpage problem during encapsulation. PMC is also one of the principal tools to mitigate outgassing. PMC can remove the volatiles from the cross-linked plastic material. If the volatiles are not removed and the EMC is exposed to elevated temperatures with poor ventilation, one will observe deteriorations in strength, elongation, compression set properties accompanied by chemical decomposition. Insufficient or poor PMC can result in “smoke”, bubbling, delamination and unsightly sticky surface deposits.

       To achieve a satisfactory PMC process, the furnace must be tuned to optimize the cure process, which can only be achieved through high quality temperature control.

Furnace Selection of PMC

      Selecting a suitable furnace requires knowledge of the temperature, time and atmospheric conditions of the process. Basically, PMC furnaces can be divided into batch furnaces and continuous furnaces. Batch furnaces are suitable for any part size but limited with respect to production volume. As batch furnaces use the same door to load and unload the part, these furnaces can only produce one batch at a time. A continuous furnace uses a conveyor-belt to continuously move parts through the furnace. So it is suitable for high volume production. Figure 3 shows a Hengli continuous belt furnace.

Fig 3. A Hengli continuousbelt furnace

      Furnace technology, economics and part quality influence the decision of using a continuous or a batch operation. The economics questions center around cost of ownership, which can include initial cost, operating costs, repair costs, product yields and return on investment. Quality issues often are associated with process stability, quality and consistency, while technology focuses on ease of operation, process definition, thermal cycles, temperature requirements, atmosphere conditions, weight of product and desired throughput. Issues and their relative importance depend on different situations.

      Most producers are still using batch furnaces for PMC process today, but as many studies and discussions have pointed out, it is better to use continuous furnaces for PMC process if one wants to get a steady flow of incoming parts.  This is because continuous furnaces are extremely versatile and can be employed to perform a multitude of processes. They are an excellent choice for manufacturing medium and high volume products. There are a great number of advantages of converting the batch process to continuous, such as:

      1) Superior art to part temperature uniformity;

      2) Increased throughput;

      3) Process combination;

      4) Lower up-front investment;

      5) Reduced changeover times;

      6) Part loading flexibility.

      A continuous furnace is ideal for processes requiring high production volumes, process consistency, and precision control. All components can go through the furnace smoothly. And during the furnace process, as the continuous furnace can serve consistent heating process, the consistency of products could be ensured in a high level. The defects will also be effectively prevented and eliminated. Furthermore, a continuous furnace can greatly improve the production efficiency by being continuously available, rather than intermittently (as is the case for the batch furnace, which must heat up and cool down). In addition, a good continuous furnace is often much more compact than a batch furnace, which is beneficial for floor space considerations and facility costs. Moreover, a continuous furnace is easily used for automation offers.

      When choosing continuous furnace, the air convection heating function should be considered, too. Unlike the traditional furnace using radiative heating, a hot air convection furnace can elevate the temperature through convective heating, which offers an extreme uniformity to PMC process. Figure 4 illustrates the difference between traditional radiative heating and convective heating. More important, the hot air convection furnace can get higher energy efficiency than conventional ovens. Additionally, with no noise and pollution operation, a convection furnace is environmental friendly.

Figure 4. Radiative heating process and convective heating process

Furnace Control of PMC

      For most PMC process, the longer cure profiles require longer furnaces. These furnaces are more suitable for the inline, integrated manufacturing line used by many printed circuit board assemblers. The PMC process needs specific control of temperature and time, which is critical for getting excellent performance after PMC process. If the temperature of furnace during PMC is higher than the setting point, components are likely to be damaged, which will cause production failures. And if the furnace temperature cannot reach the required point, the post curing would be insufficient which will lead to a great reduction of PMC quality. Consequently, it is vital for furnace temperature control to achieve high quality PMC performance.

      As the PMC process is sensitive to the temperature, uniform furnace temperatures are essential for the PMC process. For most cases, 5.6°C (10°F) is the greatest temperature difference between the hottest and coldest point in an oven that can be tolerated. Generally, a hot point occurs near the air intake while a cold point near the exhaust vent.

      Controllers programmed to raise the temperature by 0.3°C (0.5°F) per minute are recommended. Automatic shut-off and manual reset features are also desirable. A good oven is supposed to cut off automatically when the temperature reaches 2.8°C (5°F) above the set point. This is required to avoid distortion of the parts which can occur if the temperature exceeds the deflection temperature of the part.

Belt Furnace for PMC

      The HSF series hot air convection furnace is an efficient belt furnace designed and used for post mold cure process. This furnace can make temperature to 400°C. It can heat by infra-red and/or hot air circulation heating depending on your process parameters and requirements and the temperature  profiles  are  able  to  run  at  the  desired  heating  rate  to  meet  the  required PMC temperatures under controlled atmosphere.  Its air or nitrogen atmosphere can serve a completed curing process. Temperature control zones offer precise control allowing the furnace  to  run  at  the  proper  heating  rate  to  meet  the  needs  for curing. The HSF series belt furnace can offer uniform temperature distribution to meet the qualifications of PMC process. Its conveyor system allows proper heating across the belt with little temperature variations. And the HSF series furnace comes with an ultra-clean heating chamber, which can give rapid thermal response. Figure 5 shows a HSF series furnace.

Figure 5. A Hengli HSF series hot air convection belt furnace

      The furnace is long enough to handle PMC process. To  ensure  proper  practice  for  continued  use, technical information and training will be given upon  installation  of  the  furnace. A microprocessor based PID controller provides appropriate system control. Type K thermocouples are used in determining the zone temperatures. The central processing unit (CPU) is located at the entrance table and is available with a Windows operating system for ease of use and the program is installed ready to control furnace parameters such as belt speed, zone temperatures, and atmospheric conditions. Temperature profiles can be stored and retrieved as well for future purposes. There are programs for capturing/storing, displaying, and printing out the furnace profile which is already included in the software. Additionally, the furnace is equipped with a redundant overheat safety protection system which incorporates an additional type “K” thermocouple in the center of each controlled zone and the multi-loop alarm.

Conclusion

      PMC is an important technology for electrical industry. It can highly improve the properties of chips and is widely used by a great number of companies. A large number of electronic products and companies have used PMC for better performance. The quality of PMC process is deeply influenced by the temperature and time, which are strongly influenced by the furnace. A good continuous belt furnace with precise control and convective heating will offer great conditions for PMC process. 

For more information, please check http://www.beltfurnaces.com/index.html