Multivacuum and Dynamic Profiling

Transcription

1 Multivacuum and Dynamic Profiling the new reference for efficient voidfree SMD vacuum soldering process Worldwide leading in vapor phase soldering technology

2 Formation of Voids What are Voids? Crystalline residues of fluxes Gas bubbles from outgassing processes of solvents from solder paste Outgassing from non-completed polymerisation processes in and on the circuit board (e.g. solder resist) Embedded humidity from modules and component materials Reactive gases arising while removing the oxide layers with fluxes Trapped air from printing and mounting process (scooping out the solder paste with a squeegee in case of missing squeegee support)

3 What are the negative influences of Voids Restricted heat flow from components to the circuit board (heat sink) Reduced strength of solder joints Reduced vibration stability Restricted performance in the high frequency range Reduced electric capacity of components (e.g. powermodules)

4 Measures to reduce the voiding rate before soldering Using optimised solder pastes Applying special stencil geometries in the printing process to prevent the solder paste from being scooped out during printing - Good: for example star- or cross geometries known as drainage print - Bad: for example flat, grid-shaped or pointed geometries Exact fitting of the solder paste volume to the pad geometry Drying process for modules and components Avoid tempering PCBs as this increases oxidation Use metallisation with a low level of oxidation By optimising all above mentioned parameters, void rates between 10% and 15% can be achieved in a series production.

5 Measures to reduce the voiding rate during soldering Applying the vapour phase - vacuum soldering technology / MULTIVACUUM Ensuring an exact reproducible soldering profile that is optimised to the product by DYNAMIC PROFILING By using the vapour phase - vacuum soldering technology, voids can be reduced to less than 1% in the series. This applies even to large-scale soldering areas.

6 How the vacuum works Negative pressure enlarges voids -> Moving towards edge of solder joint By a further growing the void breaks through the liquid meniscus The void gets evacuated and becomes smaller, the ventilation-channel closes When returning to normal atmospheric pressure, the remaining void is compressed into its final minimised size. Cooling down the solder joint and freeze the void-less condition. Example: behavior of a balloon in the hermetically sealed glass cylinder at high and low pressure

7 Trends and Limits of Vacuum Soldering Increasing solder pads lead to larger air volume that gets trapped in the solder joint during printing and pick and place process (e.g. scooping out the solder paste with a squeegee in case of missing squeegee support). If these voids don t get removed this will cause solder splashes besides the already mentioned negative influences. Additionally the increasing solder pads and corresponding higher volume of solder paste cause major difficulties in evacuating these voids by only one single vacuum step. The various viscosities depending on different soldering alloys have significant influences on the agility of voids during vacuum process.

8 The Solution: MULTIVACUUM Several fully adjustable vacuum steps allow an optimisation of the vacuum process to the requirements of the specific product. Step 1: The adjustable vacuum step before soldering Encapsulated air from the printing process gets removed. There is no thermal process during this step. Certain solvents from the solder paste evaporate already at this point. Step 2: One or several vacuum steps after soldering Final pressure and dwell times can be adjusted to the specific product requirements. A double-vacuum step after soldering is especially recommended for very large-scale soldering areas.

9 Function Pre-Vacuum Large voids from printing process get removed before soldering process

10 Function double vacuum after soldering process Step 1 brings void to the edge of the solder joint Step 2 evacuates the void completely Solder joint before vacuum Result after double vacuum process

11 Supporting the Vacuum Process The results from the MULTIVACUUM process can be assisted and improved by a product optimized temperature profile. DYNAMIC PROFILING allows achieving this product optimized temperature profile very easily. +

12 The product optimized soldering profile The Challenge of the Soldering Process Automatic setup and adjustment of soldering profile Real time measuring of each soldering process on product level Constant profile for each soldering process Traceability in the sense of quality management Applicable from batch size one to serial production Simple adjustment of soldering profile based on nominal values

13 Parameters of the soldering profile 1. Preheating: t1 t2 Power setting (ETR) for adjustment of preheat gradient 2. Soak zone: t2 t3 Start temperature of soak zone in C. soaking time in sec. 3. Soldering: t3 t4 Power setting (ETR) ) for adjustment of soldering gradient 4. Time above Liquidus: Soaking time (sec.) after reaching end temperatur t4 t5 T in C 4 T3 2 3 T2 1 t6 T1 t1 t2 t3 t4 t5 t in sec.

14 The Solution: DYNAMIC PROFILING Using a measuring standard that is heated up together with the PCB in the soldering system. - The temperature profiles of measuring standard and PCB are nearly identical - A thermocouple for creating a temperature profile is embedded in the measuring standard. - Before each soldering process, the measuring standard is actively cooled down close to product temperature (room temperature). The temperature- / time behaviour (warming up) of the measuring standard is used as a setting for regulating the profile via SPC-control. - The temperature profile is permanent controlled during each soldering process. - Influences on the process such as different loading or different temperature of the work piece carrier are compensated. Full traceability and control of soldering profiles is guaranteed at any time by using the softwaretool ASSCON BDE/SQL-Database.

15 DYNAMIC PROFILING

16 Setting up a Soldering Profile in Practice 3 1 G B 2 Procedure for new products with DYNAMIC PROFILING: The reference PCB (golden board/gb) gets stored. Temperature profiles of reference PCB and measuring standards are recorded. Then, this measuring standard is selected, whose profile matches the reference PCB best. The required soldering program is created and the chosen measuring standard is selected.

17 Archiving Soldering Profiles (ASSCON-BDE / SQL-Database All relevant process data, as well as temperature profiles can be stored and archived with the data collection software. Possibilities of Application Traceability Soldering Profile Optimisation Golden Board Measuring Process Visualisation

18 Examples of Profiles from Practice Linear- and Ramp Profile Different Gradients Different Soak Times Different Times above Liquidus Various Holding Temperatures Profiles for leaded and lead-free soldering Compensating different Starting Conditions Repeatability

19 Linear- and Ramp Profiles Comparison: Linear- and Ramp Profile Linear- and ramp profiles can easily be realised depending on the product requirement

20 Infinitily variable Gradient Various Gradients The gradient can be adjusted to the specific product requirements

21 Various temperatures of the soak zone The starting temperature of the soak zone can be adapted to the product requirements, e.g. for different outgassing temperatures of solder pastes. Comparison: High and low starting temperature of soak zone

22 Different Soak Times The soak time can be adapted to the product requirements, e.g. for an extended outgassing of solder paste to archieve lower voiding rates. Comparison: Short and long soak times

23 Different Times above Liquidus Comparison: different times above Liquidus t1 < t2 Time above Liquidus is individually adjustable depending on the product requirements 23

24 Soldering with and without Vacuum Soldering with vacuum minimises the voiding rate The vacuum treatment starts after the soldering process has finished It is possible to achieve a voiding rate of below 0,1% during soldering of BGAs, flip-chips, power modules etc. Comparison: Identical soldering cycle with and without vacuum.

25 Leaded and Lead-free Soldering in same machine Max. soldering temperature, leaded T1 Max. soldering temperature, lead-free T2 T - leaded is slightly higher depending on the product, as the soldering process is aborted before reaching the evaporating temperature. Comparison: leaded and lead-free soldering cycle with identical vapour temperature (Galden LS230)

26 Comparing different Starting Conditions e.g. cold / hot work piece carrier If the profiles are compared to each other (superimposing), the consistent behaviour in the relevant areas becomes visible. T = T Cold work piece carrier = T Hot work piece carrier

27 Precicion of Repeatability This picture shows the precision of repeatability for a sequence of seven soldering cycles. T2 T1

28 Thank you very much! This presentation is copyrighted material owned by ASSCON Systemtechnik-Elektronik GmbH, Messerschmittring 35, Königsbrunn, Germany.