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DIMM Removal Video.mov
| Barrel Cleaning Video.mov | DIMM Removal Video.avi | Barrel Cleaning Video.avi


 
 

Next Generation Solder Fountain Technology
Designed specifically for lead-free rework of plated-through-hole (PTH) components on large, high thermal mass assemblies. The PCBRM100 uses proprietary technology that significantly reduces copper dissolution.

Key Features/Benefits:
The 24" x 26" board carrier includes a pull-out feature to provide ergonomic loading/unloading of heavy boards (figure 1) and a tilt-up feature to allow operator access to the bottom of the board for fluxing and positioning bottom side supports (figure 2). The carrier is programmable in the "X" and "Z" axes and uses linear encoders for accuracy and repeatability. Spring-loaded carrier arms allow for thermal expansion of the large board during rework.

Tilt Up Carrier
Figure 1: Ergonomic Loading/Unloading Slide and Tilt-Up Board Carrier

Carrier Down
Figure 2: Board Carrier in Position

The EZ-Line alignment system features a down-looking digital camera with zoom lens mounted on a programmable "Y" axis that superimposes the image of the solder stack over the top of the board (figure 3). X/Y joystick-based controls (figure 4) are used to quickly and accurately align the component with the solder stack (figure 5). The desired rework position can be taught on-the-fly or stored in the program.

Unaligned
Figure 3: Unaligned

Joystick Controls
Figure 4: Joystick Controls

Aligned
Figure 5: Aligned

A 28" x 28" quartz composite top and bottom IR preheater (16Kw) with 25 watts per square inch heating density and independent temperature control provides rapid, uniform preheating of even the largest, most thermally challenging PCB's. The preheater panels have an extremely high radiant efficiency and do not depend on external reflectors. The top preheater panel has s programmable "Z" axis which allows the preheater to "sandwich" the PCB based on its topside topography, thereby creating a high-efficiency oven-like preheating effect (figure 6). A thermocouple attached to the PCB provides temperature-based preheating control for process repeatability.

Quartz Preheater
Figure 6: 28" x 28" Top and Bottom Preheater with Temperature-Based Preheating

The heart of the PCBRM100 is a cast iron solder pot with titanium pump components (figure 7). No coatings of any kind are used to handle the aggressive nature of lead-free solder alloys. The pot has a solder capacity of 90 pounds and is nitrogen inerted. An internal chambering system along with a servo-motor driven pump creates a laminar solder flow with extreme thermal uniformity across the wave (+/-2˚C). Quick change titanium solder stacks direct a flow of solder against the lead pattern of the component to be reworked (figure 8). The solder pot is programmable in the "Y" axis and has quick electrical disconnects so that the existing pot can be removed and replaced by a spare pot with a different solder alloy.

Solder Pot
Figure 7: Cast Iron Solder Pot with Servo-Motor Driven Pump and Programmable "Y" Axis

Solder Stack
Figure 8: Titanium Solder Stack

What makes the PCBRM100 truly unique is the integrated Focused Convective top and bottom Heating systems (FCH). After the entire board is preheated, the PCB is moved to a position just above solder contact position. The programmable hot gas head brings the nozzle (figure 9) down and over the topside of the component to be reworked. The nozzle is fed by a 2Kw heater so it has the power needed to heat virtually any component regardless of size or thermal mass. A laser distance sensor (figure 10) automatically squares the nozzle to insure a correct fit over the component. Two (2), 7" convective heating blades focus heat on the bottom side leads. Each blade is fed by a 3.5Kw heating element and has a quick slide baffle that allows the heat from the blades to be sized to match the size of the lead pattern (figure 11).

Hot Gas Nozzle
Figure 9: Hot Gas Nozzle

Laser Distance Sensor
Figure 10: Laser Distance Sensor

Heating Blades
Figure 11: Universal Bottom Heating Blades

A typical removal process would be to preheat the entire board to 150˚C followed by a Focused Convective Heating (FCH) stage (figure 12) until all joints reach approximately 200˚C (as per the thermal profile) at which time the bottom side pins are immersed in solder for 10-20 seconds depending on the thermal mass of the component and PCB. Top and bottom side focused convective heating continues during solder immersion. Solder contact combined with FCH provides the maximum thermal transfer in the shortest possible time. The nozzle lifts automatically and the operator removes the component. This hybrid heating approach eliminates the requirement for 100% convective/IR heating as is done on BGA rework machines which reduces potential issues such as exceeding the maximum package temperature specifications, resin recession and board discoloration.

Convective Heating
Figure 12: Focused Convective Heating (FCH)

The PTH barrels can be cleaned immediately after the component is removed and the solder flow stops. The PCB remains in place over the solder stack with the bottom convective heating blades on. The component nozzle is replaced by the barrel cleaning nozzle (figure 13) which provides heat and vacuum to remove the solder in the barrels. The vacuum tip is made of a high temperature composite to prevent any abrasion of the pads or laminate (figure 14). A precision force sensor controls the initial touch off of the vacuum tip on the board. A vacuum sensor automatically and continuously adjusts the tip height providing non-contact barrel cleaning. Dual digital cameras provide the operator with multiple viewing angles during the cleaning process (figure 15).

Barrel Clean Nozzle
Figure 13: Barrel Cleaning Nozzle

Barrel Cleaning
Figure 14: Barrel Cleaning Heating Tube and Composite Vacuum Tip

Dual Cameras
Figure 15: Dual Digital Cameras for Barrel Cleaning

The replacement process typically duplicates the removal process where FCH occurs until the joints reach 200˚C at which time the bottom side leads are immersed in solder. However, instead of the nozzle lifting and the operator removing the component, the nozzle remains in place over the component while it is soldered in place. Using FCH in this fasion eliminates the solder contact time typically required to bring the component through an extended soak stage during both the removal and replacement processes. The reduction in solder contact time results in reduced copper dissolution. In addition, topside FCH during the replacement process improves barrel fill by providing a heated upward path for the solder to flow.

 



 

Rework Study
A rework study was conducted on the PCBRM100 to asses its capability to effectively rework challenging PTH components on high thermal mass assemblies. The test vehicle (TV) was a 180 x 200mm (7.1" x 7.9"), 3.3mm (.130") thick, twelve layer board with thirteen ounces of copper and an OSP finish. PTH components on the TV include electrolytic caps, headers and two 140mm (5.5") DIMM connectors. The DIMM connectors were chosen for the rework study due to their size, thermal mass, number of pins and known issues regarding connector body temperature.

SN100C solder was used due to its previously documented lower copper dissolution rate during mini-pot rework compared to SAC305. SN100C has a melting temperature of 227˚C, which is ten degrees higher than SAC305 (217˚C). The solder pot temperature used in the study was 272˚C which is 45 degrees above the melting temperature. Kester RF771 tacky flux was used as its formulation is designed specifically for rework. The solder contact time during PTH rework is multiple times longer than the contact time during wave soldering, therefore the fluxes typically used for wave soldering are not designed to withstand the rework process.

Multiple thermocouples were attached to the bottom side and topside DIMM joints as well as to the DIMM body. A baseline thermal profile and an alternate thermal profile were developed. The baseline profile preheated the entire board to 150˚C. The instrumented DIMM was then immersed in solder until all top side joints reached 240˚C, which took forty-five (45) seconds.

During the alternative profile, the board was preheated to 150˚C just like the baseline process. However a three (3) minute Focused Convective Heating (FCH) stage took place prior to immersion in solder. During the FCH stage, topside heating from the nozzle and bottom side heating from the universal heating blades increased the top and bottom side joint temperatures by approximately 55˚C. The FCH stage acts like an extended soak stage where the DIMM temperature is increased and stabilized and where the core temperature of the board near the DIMM is maintained.

Immersion in solder occured after the FCH process was complete, however the required contact time to achieve 240˚C top side joint temperature was significantly shorter, in this case twenty seconds versus forty-five seconds for the baseline process (table 1).

Thermal Profiles
Table 1: Thermal Profiles

Initial assembly of the test vehicles was done on a standard wave soldering system using SAC305. Kapton tape was used to protect twenty bottom side joints on one end of each DIMM site from wave soldering. These unsoldered joints represented the "as received" copper thickness for each DIMM site. An additional twenty joints were protected from the rework processes. These joints represented the "post-wave" copper thickness for each DIMM site.

A total of twenty-six DIMM sites were subject to a complete rework cycle that included removal, barrel cleaning and replacement using either the baseline or alternate process. Reworked TV's were sent to an independent laboratory for cross section analysis. Twelve cross section measurements of the bottom side knee were taken in the "as received", "post-wave" and "post rework" sections on each DIMM site (table 2. "X" represents ten data points).

Copper Dissolution Results
Table 2: Copper Dissolution Results (Baseline vs Alternate Process)

Table 2 shows that the "as received" copper thickness varied from a low of 1.6 mils to a high of 3.0 mils which in turn resulted in a wide variation of both the "post wave" and "post rework" copper thickness.

Table 3 is a summary of the average copper thickness and average dissolution based on the data points in Table 2. The key point in Table 3 is that the average "post rework" copper dissolution for the alternate (FCH) process was 0.5 mils compared to 0.9 mils for the baseline process. Convectively heating the DIMM prior to solder immersion resulted in a 45% (0.5 vs 0.9 mils) reduction in copper dissolution. Table 3 also shows that the average "post rework" copper thickness for the alternate (FCH) process was 1.5 mils which is significantly above the minimum standard of 0.5 mils (12.7 microns). Comparatively the average "post rework" copper thickness for the baseline process was only 0.7 mils which is just above the minimum standard. In addition, 22% of the baseline copper thickness measurements fell below 0.5 mils. Tables 2 and 3 clearly show that the alternate (FCH) rework process significantly increases the lead-free PTH rework process window for high complexity assemblies.

Copper Thickness at Knee
Table 3: Average Copper Thickness (at Knee)

Figure 16 illustrates the typical baseline rework process where significant copper dissolution has occured on the knee, barrel and pad, however the post-rework copper thickness still exceeds the 0.5 mil (12.7 micron) minimum standard. Figure 17 illustrates the worst-case baseline rework process where almost complete copper dissolution occured at the knee. Figure 18 illustrates the typical alternate (FCH) rework process where minimal copper dissolution occured.

Baseline Rework
Figure 16: Baseline Process (Significant but Acceptable Cu Dissolution at Knee)

Baseline Process
Figure 17: Baseline Process (100% Cu Dissolution at Knee)

Alternate Process
Figure 18: Alternate Process (Minimal Cu Dissolution at Knee)

In addition to copper dissolution, iNEMI also cited barrel fill as a key concern for lead-free PTH rework on Class 3 assemblies. Laboratory analysis of barrel fill on "post wave" solder joints varied widely from a low of 44% to a high of 100% with an average barrel fill of 76% (figure 19). In addition, 31% of the "post wave" joints did not create a complete fillet where solder climbs the pin (figure 23). It is important to note that the pin protrusion on the TV's was virtually zero which is perhaps a worst-case scenario for barrel fill and fillet formation. However, despite this fact, the "post rework" barrel fill and fillet results were excellent. 100% barrel fill was measured on all but four of the one hundred and fifty-six measurements taken (figure 21). In addition, a positive fillet was formed on every "post rework" joint that was analyzed (figure 22).

Post Wave
Figure 19: Post Wave Barrel Fill

Fillet Negative
Figure 20: Negative Fillet from Wave Soldering

Post Rework
Figure 21: Post Rework Barrel Fill

Fillet Positive
Figure 22: Positive Fillet from Rework Process

100% barrel fill was a key objective of the alternate (FCH) process. It was expected thet Focused Convective top side heating of the component would significantly improve barrel fill by creating a heated upward path for the solder to follow. However 100% barrel fill was also achieved in the baseline process where no FCH was used. It was surmised that there were two reasons for the significant improvement in barrel fill during PCBRM100 rework compared to wave soldering. First, the solder contact time during rework is multiple times longer than in the wave soldering process. Second, flux was applied to the bottom side of the board, the top side of the board and onto the replacement component pins during the rework process compared to just the bottom of the board during wave soldering.

A "post rework" void analysis was also performed on the one hundred and fifty-six (156) joints that were analyzed. 42% of the joints analyzed had zero voiding, 44% has a worst case void diameter of 10% or less and 14% had a worst case void diameter over 10%.

Summary and Conclusions
The solder fountain or "mini-pot" has been the industry standard for tin-lead PTH rework as well as lead-free rework of PTH components on low and mid-complexity assemblies. The solder fountain process has been optimized for lead-free rework by the use of lower dissolution solder alloys and by the addition of integrated preheating systems. In addition, BGA rework systems with convective and IR heating systems have been successfully used to remove lead-free PTH components for applications where the optimized solder fountain process does not meet the rework objectives.

The current "lead in solder" exemption for Class 3 applications including server, storage and network infrastructure equipment is set to expire in 2014. Alternative rework solutions, including convection, IR, vapor phase and laser have been proposed, however none of the existing technologies was designed with lead-free rework of PTH components on large, high thermal mass assemblies in mind.

The PCBRM100 is a "clean sheet of paper" design approach to solving copper dissolution and barrel fill issues on Class 3 assemblies. In design and beta testing for over three years, initial production shipments will begin in the first quarter of 2013. The key to the PCBRM100 is the top and bottom focused convective heating (FCH) system which significantly reduces the required solder contact time which in turn significantly reduces copper dissolution. A two phased DIMM connector rework study on the 100 demonstrated that 100% of DIMM connectors reworked with the FCH process showed excellent results in regard to "post rework" copper thickness, barrel fill and fillet formation. Void analysis showed excellent results on 86% of the joints analyzed, however some large, random voiding did occur. The combined phase one and phase two processes were based on the complete rework (ie. removal, barrel cleaning and replacement) of twenty-six (26) DIMM connectors with fifty-two (52) cross sections, nine hundred and thirty-six (936) copper thickness measurements taken and one hundred and fifty-six (156) barrel fill and voiding calculations made and fillet formations assessed.

 

Specifications
• Machine Dimensions: 120"L x 52"W x 77"H
• Maximun Board Size: 24" x 26"
• Solder Pot Capacity: 90 pounds
• Preheater Size: 28" x 28" (top and bottom)
• Maximum Component Size: 8"
• Top Side/Bottom Side Clearance: 3"
• Reflow Access: 24"(X) x 16"(Y)
• Thermocouple Channels: 8

Available Certifications (additional fee)
• ETL
• CE

Facility Requirements
Electrical
• Machine Power: 208-240 VAC, 50/60Hz, 3-phase, 60 amps
• Monitor Power: 220V, provided by convenience plug on machine
• Computer Power: 220V, provided by convenience plug on machine

Electrical: IMPORTANT
• This system is designed to operate on 220 VAC, 3-phase
• Under full load conditions, power must not drop below 208 VAC. Verify all 3 phases.
• Under no load conditions, power must not exceed 240 VAC. No load is defined as PCBRM100 off and all other equipment down line turned off.
• In areas susceptible to frequent power disturbances, line filtering/protection may be required.

Air/Nitrogen (Base Machine)
• Main Air Supply: 90-120 psi, 25 scfm, clean, dry air
(non-condensing) source.

General: These requirements must be addressed prior to the installation and training visit.
This will assure you receive a productive training program within the scheduled installation time.

Technical Data Subject to Change.


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
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