With electronic assembly continuously evolving it is paramount that systems are put in place that can meet today’s requirements and expectations, whether that be ensuring quality or simply cost saving.
One system that has improved production significantly is thermal profiling. Traditionally a profiling instrument is used to establish the correct thermal profiling for the soldering process. Thermocouples are attached to a PCB (Printed Circuit Board), and the component level temperatures are captured by the measurement datalogger.
Verification profiles are then captured on the SMT (Surface Mount Technology) line by periodically passing the test PCB and instrument through the process.
The Need for an Automatic System
Until recently the preferred and only way to manage assembly was through manual profiling, recent innovations in the area of automatic profiling technology has resulted in increased levels of process quality and less need for labour intensive manual profiling. The need for regular monitoring of temperature profiles has always been an important consideration, and past methods included obtaining temperature profile through attaching thermocouple sensors to the PCB and recording temperature profiles using a heat protected datalogger, which travels through the process behind a test PCB. Although this method appeared to work effectively for initial machine set-up, it does not lend itself to ongoing process monitoring in high production rate environments, something becoming ever more important.
As this system could only be deployed periodically manufacturers were faced with having to manually take a reading at different times in the process and hope that in-between this time the process continues to work effectively – this of course was not a guaranteed process and was based on ‘hope’. Not only was the process unreliable but every time a reading was taken production had to be stopped to allow the test board and profiler to pass through. If a problem did occur, it would only be discovered when the next reading took place, and if incorrect it would involve loss of production time to rectify the situation.
Developing the APS
To combat this rather inefficient method, the SolderStar Automatic profiling System (APS) was designed. SolderStar first developed the APS-1000, which measured the stability of the process parameters within a reflow oven. Designed with a rigid thermocouple tube with internal thermocouple sensors mounted at the desired position, it measured the zone temperature at product level. Although it was very robust and was a far cry from the manual method, it still had disadvantages. It was found the response time was slow and there were conduction problems between zones. It was also extremely expensive to manufacture and caused problems to distribute overseas. The physical diameter of the probe was also undesirable on bigger machines and could potentially cause shadowing of the product as it passed through the process. This obviously was not ideal and although taking the right step forward a newer, more reliable system was required.
The New and Efficient APS is Developed
SolderStar worked on improving this process and designed a profiling system that did not have the flaws of its predecessor, and so the APS-2000 was developed. The new system was the first product offering to measure the stability of the process parameters within a reflow oven, combined with assembly position tracking to produce the most representative virtual profile possible for every PCB passing through the machine, a breakthrough for the industry. The APS 2000 continuously tracks PCB movements through the machine and also monitors process fluctuations at product level. These changes are then used by a mathematical model to calculate what the resulting PCB profile would be, this is known as the virtual profile. Process parameters can then be calculated and tested within limits.
This system has been worked on, re-designed and improved over the years and is quickly catching the attention of manufacturers across the globe. Two years ago a round of development took place and a new design was produced which solved previous problems. The original APS product was based around the same instrumentation circuits used in their profiling systems, but due to research and experience it was understood that a new instrumentation circuit could be developed that was specific to the needs of the systems. The new electronic measurement system deployed in the APS 2000 would reduce the number of thermocouple conductors required to make the measurements needed. This allowed for a much smaller probe diameter to be achieved. For example on a 16 zone machine a probe diameter of typically 6mm could be used.
The response time of these probes is exceptional, allowing the detection of machine faults quickly and easily so they can be rectified, saving both time and money.
Faults the APS-2000 can detect:-
- Zone temperatures set incorrectly from a defined reference
- Speed set incorrectly from defined reference
- Oven zone feedback thermocouple failures
- Fan failures
- Conveyor speed failures
- Incorrect oven recipe loaded by operator
- Overloading of oven throughput
- Thermal profile outside process limited
This combination of benefits has given manufacturers peace of mind and helped to improve manufacture. It is because of this that most recently two leading European manufacturers have decided to invest in the APS 2000, after successful long term and comprehensive testing of the system.
The SolderStar APS is a full time system for profiling each and every PCB soldered in a convection reflow oven. The system is tailored for, and fitted, to a customer’s oven so their requirements are met precisely. The system works by continuously measuring product level zone temperatures and conveyor speed and comparing these measurements to a captured process reference which the system has previously learned.
The system continuously compares each new set of measurements with the reference and evaluates any differences.
Should the difference between the current process and the reference exceed user defined limits, then further boards are prevented from entering the oven by way of the SMEMA (Surface Mount Equipment Manufacturer’s Association) interface.
Special temperature probes are mounted along the heated length on both sides of the machine to monitor actual product level temperatures in real time. In addition to this, the system keeps track of the current speed and position of each assembly in the process.
The temperature probes have been designed to be smaller, and can be positioned closer to the PCB providing a much more accurate temperature measurement in the vicinity of the electronic assembly during soldering. The smaller size also reduces the danger of the probe shadowing the product.
Why measure independently of the oven?
The APS system measures the product level zone temperatures and conveyor speed independently of the oven. This is important for two reasons:-
Firstly the machine may malfunction for example a heater or fan may give trouble.
Secondly, an operator may load the wrong recipe for the board being produced.
Why measure temperature at product level?
The oven itself monitors and maintains the temperature of each zone. This measurement is made near to the heaters and does not closely reflect the temperature seen at product level which is a function of the machine convection.
The APS system adds independent temperature sensors mounted at product level close to the conveyor rails. These sensors are designed to closely measure the heating levels impinging on passing circuit boards whilst at the same time minimizing shadowing caused by the sensor itself.
As a PCB enters the reflow oven, its progress is tracked through and temperatures recorded at product level sensor as the PCB goes through the zone.
When the PCB exits the oven, the profile is mathematically calculated using the live measurements, and the PCB reference profile, it is then evaluated PASS/FAIL and recorded, making the results easy to follow.For each PCB there is a record of the process speed, and each zone temperature and the mathematical profile, so again 100% traceability is available.
Traceability, barcoding and SMEMA integration
Where barcoding is available the APS can also integrate with internal enterprise resource planning (ERP) systems to provide automatic storage of PCB data from the production lines. Because there is barcode integration it allows the profiles in the database to be tied to a specific PCB produced, ensuring 100% traceability. It also has SMEMA functionality which allows the APS to control the flow of product into the reflow oven, these two features make a very powerful system.
Additionally there is the ability to automatically detect product changeover on the production line, as the PCB moves along the in-feed conveyor to the oven, the PCB barcode can be scanned and fed to the APS system. The PCB assembly type can then be determined by the APS and a decision made if the process is correct for that assembly, if not the PCB will be held on the in-feed conveyor and an engineer notified. Once the oven has been changed over to the correct settings for the new assembly being produced, the APS will wait until all parameters are stabilised before allowing the flow of product to continue.
When barcoding is employed, a virtual profile and all oven conditions are recorded for every assembly which can be later retrieved to provide total traceability of each assembly produced.
| APS SHOWING BELTSPEED ERROR AND PROFILE OUT OF TOLERANCE |
When the APS 2000 is used it follows specific steps to calculate profiles in real-time.
Step 1: Capture the actual profile from a PCB using a test PCB and manual profiler
(This gives the software the thermal model of the oven and the components/PCB)
Step 2: The APS 2000 analyses and records the ‘good’ state of the reflow oven
Step 3: The system measures in real-time any fluctuations in the process. The information from
Steps 1 and 2 are then used to calculate the resulting profile. Process parameters are also calculated and tested against defined limits.
The APS System Advantages
- Provides full time monitoring of reflow soldering process which does not rely on repeated profiling.
- An easy to understand system concept. ‘PROCESS TEACH then TEST’
- Simple to install and operate
- User Process limits allow the machine to be automatically stopped if the process drifts too far away from the reference.
- Automatic process tracking and traceability for all products produced.
Why Use the APS System?
A system like the SolderStar APS 2000 offers everything an electronics manufacturer would require in profiling. It can discover ‘problems’ as they happen which can be rectified easily and efficiently reducing down-time and man hours and is a fail safe way to ensure the PCB assembly and manufacture is correct with guaranteed traceability.
The continuous nature of the APS means that the thermal process no longer runs blind. The profile for every single PCB is measured and meets the requirements of that particular load. Being bespoke it can also work to meet strict requirements of the manufacturer lowering the cost of production by reducing production downtime due to rework and labour.
SolderStar APS has been designed to include a sophisticated computer algorithm which uses a reference profile, captured once from a traditional profiling system along with live readings from the process to calculate a mathematical profile for each PCB exiting the oven. The algorithm used by the software to produce this profile from the live readings and reference profile has been modified based on the input of a leading mathematician to yield more accurate results.
The APS system allows 100% checking of temperature profiles, an automatic analysis of the profile, and checking of production parameters against production limits. The computer software tracks the progress of the PCB through the oven allowing for the most accurate calculation of the profile seen at product level.
This latest system has captured the attention of major blue-chip companies and with continued developments and features introduced to the system it is gathering pace and becoming a real benefit to the electronics production industry.
