Dispelling the Black Magic of Solder Paste

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Solder paste has long been viewed as “black magic”. This “black magic” can easily be dispelled through a solder paste evaluation. Unfortunately,solder paste evaluation can be a challenge for electronic assemblers. Interrupting the production schedule to perform an evaluation is usually the first hurdle. Choosing the solder paste properties to test is simple,but testing for these properties can be difficult. Special equipment or materials may be required depending upon the tests that are chosen. Once the testing is complete,how does one make the decision to choose a solder paste? Is the decision based on gut feel or hard data? This paper presents a process for evaluating solder pastes using a variety of methods. These methods are quick to run and are challenging,revealing the strengths and weaknesses of solder pastes. Methods detailed in this paper include: print volume,stencil life,response to pause,open time,tack force over time,wetting,solder balling,graping,voiding,accelerated aging,and others. Hard data is gathered and used in the evaluation process. Also presented in this paper are a set of methods that do not require expensive equipment or materials but still generate useful data. The goal is to help the electronics assembler choose the best solder paste for their process.

Author(s)
Tony Lentz
Resource Type
Technical Paper
Event
IPC APEX EXPO 2015

The Role of Organic Amines in Soldering Materials

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The transition from eutectic tin-lead to lead-free soldering in electronic assembly,mandatedby the RoHS legislation, has brought great pressure and challenge to solder material formulationdue to the high soldering temperature and high alloy surface tension. Moreover,the demand for halogen-free materials,which should be transparent toprocess yields,along withtheminiaturization trend in the electronic industry,is triggering arevolution in solder flux and paste formulations.The chemicalandmaterialinteractionsrelatedtosoldering andassemblyprocesses are many and varied. In general, the chemicals have to bestable during handling at mild temperaturesto warrant a process-friendlyshelf-life.Whileatpreheatandsoldering temperatures,thesolderfluxort h e pastehave to provide thermal transfer to the joint area and reactwiththemetallizationontheprintedcircuitboard(PCB) andcomponentleadstoremoveoxideandsurfacecontaminationinordertopreparethesurfaceforgood metallurgicalbonding,prevent re-oxidation with the atmosphere until the solder alloy re-solidifies,and promote wetting to form the joint.Residuescreatedbythefluxcontainmetalsalts,aswellasorganicandinorganic byproducts.A traditional formulation mainly relies on organic-based materials,rosins and carboxylic acidsto promote fluxing.Several attempts to understand the reactivity of organic acids and halogenated species have demonstrated the complexity of the chemical systems involved in fluxing mechanisms. Amine based formulations were mostly found in the old days,in the forms of ammonium orammonium halides. Here,we report a preliminary study aiming at giving some insight into the role of amines in electronic assembly applications. Our work shows that practical tests can be developed to characterize some fundamental properties of the activator packageswhich directly impact the final performance. The studyofinteractions between individual components within the systemis another key aspect of the design work.From that perspective,we intend to demonstrate that the formulator can develop robust formula based on scientific principles and rational studies rather than empirical knowledge and trial-and-error approaches.

Author(s)
Yanrong Shi,Xiang Wei,Bruno Tolla
Resource Type
Technical Paper
Event
IPC APEX EXPO 2015

The use of an available Color Sensor for Burn-In of LED Products

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In today’s world it is important that a product has sufficient accreditation that it can be enter many different market places. While accreditation can be a costly process,it is prudent to know that your product is fit for purpose before going for accreditation. We propose a novel cost effective system for testing 100% of the LEDs (Light Emitting Diode) on a lighting product. This system will not only monitor the intensity and colour changes of a product while it is running but alert the engineer of early failures allowing the test to terminate,and faults to be examined. We propose this system as a rapid prototype tester. This system also allows unique LED changes to be monitored such as one LED to noticeably change while not changing the macro properties of the lighting unit. While a small change in individual LEDs or a small group of LEDs in a lighting product might not affect the accreditation process,it could have warrantee effects when the product is in the market
place. We will introduce the system,and show the results of five different LED based products being tested simultaneously over the course of three months. Each product consists of twenty LEDs,so we will monitor 100 LEDs simultaneously. The results will show unexpected behaviour of the LEDs,over the period of three months as a case study. We will show how such a system could be adapted for Standards such as IESNA LM-80 [1] and TM-21 [2]. Lastly we will show the advantage of pre-aging LED products to allow for improved lifetime estimation. While not a replacement for standards such as IESNA LM-80 [1] and TM-21 [2],the technique outlined above would allow smaller companies increased confidence in their product when getting a product range accredited. The system allow shorter prototype development times and hence a cost
saving to end-users.

Author(s)
Tom Melly
Resource Type
Technical Paper
Event
IPC APEX EXPO 2014

SJIT,Solder Joint Integrity Test,To Find Latent Defects in Printed Wiring Board

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To find defects of solder joint in printed wiring board assembly,quite a few test methods have been developed so far.
Capacitance method and IEEE 1149.1 or boundary scan method are often used to find opens between component leads and
pads on a printed wiring board. These methods,however,can find complete opens or complete shorts only. Latent defects that
can be complete defect after several years have not been found by the conversational method.
We have developed a method to find such latent defects by using 4-wire small resistance measurement technique and have
built in a flying-probe in-circuit tester. It measures the resistance between component leads and pads,and checks the volume
of the solder. Because the volume of the solder is inversely proportional to the resistance in-between,resistance measurement
can be a way to test the solderability.
This technique is industry proven. A lot of manufacturing plants which produce printed board assembly used in automotive
have adapted it. The printed wiring board assembly for automotive must endure vibration. Thus if a board assembly has a
latent defect,it can bring a serious accident. In my presentation,I would like to introduce the importance of SJIT,Solder Joint
Integrity Test,and a technique of SJIT.

Author(s)
Hiroshi YAMAZAKI
Resource Type
Technical Paper
Event
IPC APEX EXPO 2014

Reduce Design Time and Product Lifecycle Costs with Functional Blocks Common to Designs and Test Fixtures

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This paper proposes an integrated design and test strategy which uses functional design blocks common to both designs and test fixtures,with the aim of saving time and money. Benefits of this strategy include reducing total product lifecycle cost by decreasing product and test development times,improving sustaining engineering processes,and reducing unique component counts across products and test fixtures.
Benefits and drawbacks to such a system are explored for a company that produces low volume,long life products. Benefits analysis is applied to software development and maintenance,schematic design,printed circuit board layout,hardware design,and fixture development for verification,qualification,and functional tests. A brief explanation is provided regarding how existing commercial functional test platforms can be inadequate in a low volume,long life integrated systems production environment. Analyses of process changes and technical hurdles that will need to be overcome while deploying such a system is examined. Finally,a phased approach is suggested that will minimize disruptions to daily operations; minimize any significant,up-front expenditure; and integrate into existing systems.

Author(s)
Stephen Golemme
Resource Type
Technical Paper
Event
IPC APEX EXPO 2014

Color Logical Analysis Approach for LED Testing in Manufacturing

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Complexity of test development for LED test and long LED test execution time in production are big challenges faced by the PCB manufacturing industry. This paper introduces a parallel multi-channel,multi-function color logical analysis (PMCMF-CLA) methodology to achieve zero additional test development and zero extra test execution time.
Traditional LED test includes two major tasks. 1. Development of test program to drive LED ON/OFF. 2. Test execution in production line. Test program development incurs a one-time cost for each type of DUT and it is a challenging job. The engineer needs knowledge of the device under test (DUT),and skills in test development. LED test execution contains several steps: driving LED on,waiting for LED to reach stable state,measuring LED,driving LED OFF. It would be ideal to save the effort of test development and time to run LED test in production.
In this case study,several PCB boards for desktop and laptop are studied. The number of LEDs varies from 0 to 20. The observation shows opportunity for zero additional test development. 70% to 80% of LEDs are lit at certain time during power-on test and functional test stage. Some LEDs are lit constantly. Some LEDs are turned ON or OFF according to time. The sampled ON and OFF forms a sequence of ON/OFF that provides information about not only whether LED is present,correct,and live,but also DUT functionality. This LED ON/OFF behavior presents an opportunity to have zero test development and zero extra test execution time.
PMCMF-CLA is a method to achieve LED coverage with zero additional LED ON/OFF test development and zero extra test execution time. PMCMF-CLA monitors multiple LEDs in parallel while other tests are running. Measurement of color (in the term of wavelength) and luminosity is recorded along with its sampled time. The sampled data forms color waveform that can be analyzed for various test purposes. For example,an expected LED has red color with certain luminosity. When it is detected in a color waveform,the information indicates the LED is present,correct and live. Color waveform analysis can be running in parallel while LED ON/OFF is monitored. Therefore,overall test execution time is almost the same as the test program that has no LED designated test.

Author(s)
Zhi-Min Shi,Yang Hua
Resource Type
Technical Paper
Event
IPC APEX EXPO 2014

AXI Applications with BTC and Connectors in Flextronics

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Bottom Termination surface mount Components (BTC) are extremely popular because of their low cost,low stand-off height and excellent thermal and electrical properties. In this manufacturing arena,more and more connectors are utilizing the printed circuit board (PCB),due to its ability to allow convenient memory expansion in servers and embedded applications in communications. The challenge for the industry is to achieve the best possible BTC and connector solder joint quality. The following questions are keys to our discussion: What is the best way to use test and inspection techniques? How does one obtain accurate AXI (Automated X-ray Inspection) data and images for surface mount technology (SMT) process improvement? How does one minimize voiding in thermal pads caused by changing design rules in order to meet stringent customer requirements? How does one reduce the use of mechanical cross-sectioning,since it destroys costly PCBs and is time-consuming?
Identifying product defects associated with the manufacturing process is a critical part of electronics manufacturing. When faced with the need for high yields,especially for new product introduction (NPI),AXI faces challenges with new packages and processes,such as BTC and connectors. In this project,we will focus on how to use AXI to identify BTC and connectors,especially for voids from AXI testing of Mosfet and PQFN packages. The test methods include AXI,2DX and cross-section. We would like to reduce destructive methods in order to have a high-accuracy,low-void percentage from DOE (Design of Experiments).
We analyzed data from Tomosynthesis of AXI3 machine,AXI4 machine and 2DX,cross-section (virtual and horizontal cross-sectioning) using QFN package types (Mosfet and PQFN). The goal is to look for a correlation between AXI and 2DX,2DX and cross-section for improving accuracy levels with AXI data. The SMT process was improved,with good feedback of X-ray data and correlation results.

Author(s)
KH Ooi,Ivan Khaw,Zhen (Jane) Feng,Ph. D.,David Geiger,Murad Kurwa
Resource Type
Technical Paper
Event
IPC APEX EXPO 2014