Rework

Thermal News recently interviewed Amanda Hartnett regarding thermal management with metal TIM (thermal interface materials). You can read the full article here:

http://www.thermalnews.com/eprints/Indium_0310.html

I really like this interview, so I’m not going to give away the best parts – I want you to read it yourself. I do, however, want to provide a couple teasers to pique your interest. I’m leaving out the especially cool parts…

“Pure indium, used as a solder TIM, delivers a thermal resistance to…”

“Also, it is important to consider the reworkability of an interface material. TIMs such as … are very simple to rework. Others, such as conductive epoxies, can be quite difficult.”

“When I measure the performance of thermal interface materials, I characterize them based on ... This value is typically more valuable than bulk thermal conductivity. For a compressible TIM, the … assumes the actual contact which will be made between the interface material and it’s mating surfaces. This provides a measurement of thermal performance which is as close to real-world per Watt or per cm2 as I can provide without being application-specific.”

Are you still reading this blog? Go read the article!

~Jim

I love watching a good basketball game, and one of my favorite local teams is the Syracuse Orangemen. If you go to a Syracuse home game, notice the shot clock – it was made with Indium Corporation solder. There are a lot of places you can see our products in your everyday life. That smart phone in your pocket, the electrical components in your car, the thermal interface in the computer in front of you. That’s one of the things that makes this job rewarding, being part of so many various applications.

In addition to learning about these different applications, we also get a good reference for what assembly trends are developing, and which material technologies are becoming more popular. 

I’ve watched the halogen-free trend explode and fade, as it was adopted by some large OEMs and their contract manufacturers, but has not spread to most other companies. Another trend that is fading away from the spotlight is Pb-free die-attach solder, since the EU has not found a suitable replacement and has pushed back the exemption deadline. 

A long-existing topic that has had recent mention is solder jetting. The trend towards soldering smaller components is not new or surprising, but for smaller components (01005s and 0201s) we have seen a trend towards dispensing instead of jetting – which seems to suit those applications.

For small component printing, transfer efficiency is critical. Outside of solder paste optimization, “nano-stencil” technology is an upcoming technology that may take-off and improve paste release characteristics. Solder paste is being used in some other creative ways too, like low temperature alloy dipping paste for rework operations. Manycompanies are now using or evaluating specialized solder applications to replace components without fully reflowing the rest of the components on the board.

Integrated preforms are finding their way into more and more applications recently as well. These connected preforms are being used to reduce the need for component pallets and selective soldering operations.

All these applications are great ways that our customers are taking soldering technology to the next level, using materials and assembly methods that were not common before. I look forward to learning how you’d like to use solder in your application!

Folks,

Every so often a new electronics assembly technology comes along, and I am asked my opinion about it. The latest “new” technology for assembly is RF Activated “Green” Nano Solder.

My response when asked about this follows:

“I think Intel's caveat in the article tells it all:
 
‘Intel cautioned, however, that several engineering refinements need to be made before the new RF soldering method can be used commercially.’

 
Interpretation: This puppy needs $20 million of R&D before it is ready.
 
Nano solders have been studied for years.  They are interesting and have promise, but there are big hurdles.
 
People will say they want an exciting new technology like this, until that find that the soldering material costs much more than their current one, they need new equipment, etc.  All of the sudden today's process (disappointments included) doesn't look so bad.  It is hard to replace an incumbent process unless there is a strong need - and typically it must be at equal or lower cost.  These will be challenges for this proposed process.
 
So my take is, it is interesting process science, but let's wait awhile to see more data, prototypes and cost estimates before we get too excited.

Any new technology process must be evaluated under the following criteria:

1.     If “disruptive”, it must meet an overwhelming need. E.g.: If your process has a 95% first pass yield and the 5% of the product that is repaired only cost a small amount, you will be unlikely to want to take a chance on a new, unproven technology when the time comes to invest money in it.

2.     The new technology’s implementation must have a minimum of disruption, if implemented in a current process and the cost must be equal or less than today’s process. E.g.: You want to improve your process in #1, however if the new process requires radically new equipment and/or materials you will be hesitant to adopt it.

3.     The process will need several years to prove itself. You know the problems with today’s process, but what are the problems with the new process? You will likely want yield and reliability data. These requirements will take some time.

4.     You must consider the improvements in the old process. Often a new process will aim at where the old process is today, not recognizing that the old process is often improving by the time the new process is implemented.

Using these criteria, let’s look at the implementation of SMT technology in the age of through-hole (TH), circa 1980. How did it measure up to these four criteria?:

1.     SMT met an overwhelming need. One simply could not design a small, high performance personal product, like a mobile phone, with TH.

2.     SMT lines evolved from TH lines, sometimes with radical changes, but the need overwhelmed any disruption.

3.     Much work was performed on SMT products to demonstrate that reliability was acceptable.

4.     The need for SMT was so great that TH's "future" was not an issue.

Contrast this situation to the SMT process discussed above (that has 95% first pass yield) with the 5% fallout reworkable. It becomes difficult to envision making any “disruptive” change to a process like this…..it just won’t pay financially or in any other way.

Your comments?

Dr. Ron

Patty, Pete, and John prepare to do battle with "The Big O."

Patty and Pete were able to squeeze in 9 holes of golf, though it was really stressful for Patty. Pete was a good golfer, but not in Patty’s league; he typically shot in the low 80s for 18 holes compared to Patty’s 68-72 range.   Today, going into the 9^th hole, Patty was even par and Pete was one under. He was teasing her relentlessly.   The ninth hole was 532 yards long. Patty used all of her recent training and focused as she drove the ball. Her swing speed hit 114 mph and with a 4 mile an hour tailwind, her drive was 291 yards, 30 yards beyond Pete. Her second shot, with a five wood was 12 feet from the pin. Her putt was dead center for an eagle, Pete’s 8 foot birdie putt lipped out of the hole. Whew! She beat Pete by one stroke! Pete was still thrilled that he gave Patty such a close call.

As they left the golf course, Pete said, “John is really working miracles at the factory, given the constraints he is working under. He has developed a disciplined approach to changeovers and uptime, and has eliminated most waste. But the factory really needs to be cleaner and more organized. With all that is on his plate, and no cleaning staff, he will have trouble implementing a 5S. It will be hard to win new customers with the place looking like it does.”

The next morning, as they prepared for the meeting with Oscar Patterson, Patty noticed that John’s color was ashen.

“John, are you alright?” Patty asked.

 “You’ve never been in a meeting with Mr. Patterson. He can be a bit…uh…. difficult,” John stumbled out.

“From what I hear he is a ruthless, brutal dictator,” Pete added.

John did not disagree.

Patty thought it might be best to call back to her site GM to clarify her mission.

The GM told her, “This guy is a blowhard, it would be great if you could review with him your findings and get his buy-in. But, don’t take any grief from him. He forgets that he sold us his company. Now he has a boss, and it is me. I told him you were going to perform an audit and I want him to work with you.”

So Patty, John, and Pete went to Oscar Patterson’s office to review their findings. Patty was immediately intimidated by him. He was a huge man with a ponderous stomach. But the posters in his office were the worst. One read “I’m the Boss, you aren’t.” Another read, “My way or the highway.” Then she saw, “The Golden Rule of Management: Whoever has the gold makes the rules.” The last one she took time to read was especially troubling: “It’s a question of mind over matter: I don’t mind and you don’t matter.”

Patterson spoke first, “Let’s get this over with, I don’t have time to waste on this nonsense. I’m the boss and I’m responsible for profits, so give me your crap and get out of here.”

The Professor always advised Patty that after an audit it is best to present the strengths first and then the problems. However, never call the problems “problems,” call them “opportunities for improvement.”  “I learned this from my colleague Joe Belmonte,” The Professor told her. She had since met Joe at a few trade shows and was impressed by his wealth of experience and in-depth knowledge of assembly processes.

She started by discussing the very good 25% uptime, and the fact that the operators were quite good at changeovers.  Pete had pointed out that the operators told him that John was responsible for both of these successes. The operators liked and respected John, but realized he had a tough job working for Patterson.

As imagined, Patterson warmed up to this compliments. 

“I told ACME management that buying my company was a good deal. We cut costs and I am able to make a profit even though I have losers like John working for me,” Patterson bragged.

Patty was furious at this comment. Pete looked like he was going to jump across the table and take a swipe at the “Big O.” John just sat there looking defeated.

“This isn’t as bad as I thought it would be,” boomed Patterson. “Continue.”

Patty then reviewed the 7 mudas. She had been surprised that the company did quite well in this part of the audit also, undoubtedly attributed to John:

1. Overproduction

2. Unnecessary transportation

3. Inventory

4. Motion

5. Defects

6. Over-Processing

7. Waiting

Hence, Patty’s comments were positive on this topic.

“You'se guys aren’t so bad,” boomed Patterson. “I told you I was good at generating profits, even stuck with a dufus like John here,” he finished.

At that comment, Pete’s faced turned the most crimson Patty had ever seen.

Patty then went on to “Opportunities for Improvement.” She thought she would start with 5S.

“We performed a “5S” audit of your facility. This manufacturing philosophy consists of:

1.       Sorting

2.       Set in Order

3.       Shining

4.       Standardizing

5.       Sustaining the Improvements,” she started.

“As ACME strives to get more customers for our contract manufacturing services, 5S is an important consideration, as many of our current and future customers practice Lean and especially 5S at their facilities,” Patty added.

As she went on she reviewed the lack of order and cleanliness in the facility. She had photos of dried solder paste on the stencil printers, the flux and dust “stalactites”, and several other examples of 5S violations. Patterson’s face soon matched Pete’s in its level of sanguinity. But he said nothing.

Patty then volunteered that she and Pete would work with John and his team to implement a 5S if desired.

Patty could see Patterson was ready to blow, but she felt she must go on. The only topic left was turning off the nitrogen in the wave soldering machine.  As Patty played the wave soldering video, surprisingly, Patterson seemed interested. 

She continued, “We think an opportunity for improvement would be to re-instate the use of nitrogen in the wave soldering process. First pass yields have dropped from 94% to 87%, thus increasing re-work. Or, perhaps, implementing a more robust wave solder flux. I contacted a wave flux vendor and I have some recommendations.”

At this Patterson became even redder in the face, in a rage he grabbed Patty’s laptop and threw it on the floor, instinctively Pete dove for the laptop, spun around and inserted his chest between it and the floor.  Patty had never seen such agility in a 45 year old man.

“You bozos are worse than John the clown here!" he shouted, as he gesticulated toward John. 

Patterson then kicked the trio out of his office. Pete was ready for a fight, but John and Patty, both visibly shaken, held him back.

Patty immediately called Sam, her GM, and told him in detail their findings and what happened at the meeting. She gave a good impression of what John had accomplished in spite of Oscar Patterson.

“Wow! Patty, I’m so sorry. I didn’t expect it would be this bad. I’ll change my schedule and fly there today. This situation will not stand. Why don’t you and Pete take a break and meet me for dinner at Dinardos at 7PM? Bring John with you.”

Patty was glad that she backed up her files last night on SugarSynch, even though it looked like her laptop was fine. 

Colonial Williamsburg was only a 45 minute drive away, and it was just 10AM. Taking Sam’s advice to “take a break,” she and Pete drove away and toured this beautiful living museum. They also had lunch at the Trellis.

Surprisingly, with the Williamsburg respite and all of the walking Pete and Patty did, they were more relaxed and hungry than they thought they would be. 

On the way back to Dinardo’s Patty asked Pete, “How did you save my laptop, I’ve never seen such an agile, athletic move?”

“Twenty-nine years of beach volleyball,” Pete answered.  “I was good enough that I tried out for the Olympics  in ’92. Humbling experience,” he added.

About 10 minutes before they arrived at the restuarant, Patty's mother called with updates on the wedding plans.....only 10 weeks and counting!

John had arrived early at the restaurant and Patty and Pete met him. He looked very nervous. 

“John, how’s it going?” asked Pete.

“It’s hard to be optimistic,” John answered.

On that note Sam walked into the restaurant.

“This must be John Davis, the new GM, having replaced Oscar Patterson,” Sam stated with great cheer.

These words didn’t seem to register with John.

“Congratulations John, well deserved,” Patty and Pete chimed in.

In the few days they were there, Patty and Pete had grown quite close to John.

As the information sank in, tears welled up in John’s eyes.

“Do you think I’m up to the job?” he asked.

“John, you are already doing the job,” Patty answered.

Epilogue:

Sam had felt it best to have the police accompany him to see Oscar Patterson with the news that he was fired. Patterson became so agitated that the police had to threaten to arrest him before he calmed down and was escorted out of the facility.

With John at the helm, the “shop” was not recognizable in 3 weeks, as he implemented a 5S program that he designed with Patty and Pete.

He performed some DOEs to find a wave solder flux that could perform well, without nitrogen, for most of his applications. However, he still used nitrogen for a few boards that had a large thermal mass. All of these, and the many other, decisions he made were data driven.

Have you performed a Lean audit of your facility? Do you regularly practice 5S and look to eliminate the 7 mudas? Are your decisions “data driven” as John’s are?

Cheers,

Dr. Ron

Conductive epoxy is a common material choice for bonding components, especially if the assembly process is temperature-sensitive. Tin-based solder paste or preforms with flux are preferred Pb-free bonding materials; however, conductive epoxies arguably provide advantages over these traditional solder assembly materials. 

It has been my experience that these advantages are perceived in the absence of an awareness of the full solder assembly materials product offering. Specialty solders can provide the same advantages as conductive epoxies and then some.   

Some claimed advantages to conductive epoxies include:

·         RoHS-compliance

·         Ease of assembly

·         No-clean

·         Low cure temperatures

Low-temperature solders such as 58Bi42Sn and 52In48Sn are specialty low-temperature solders which have these same properties including processing temperatures below 150ºC. Both of the referenced alloys are Pb-free, can-be used with no-clean fluxes and are assembled using the traditional solder assembly techniques.

It would seem a toss-up between whether to use a conductive epoxy or specialty solder to assemble temperature-sensitive components except that there are additional advantages to a soldered assembly as compared with an epoxy-assembly. These include:

·         Thermal cycling reliability

·         Solder material consistency

·         Reworkability

·         Thermal Conductivity

Click here for a description and video that shows a nozzle design from FINETECH  which clamps down onto PoP components during rework. 

“The PoP soldering head is an easy-to-use tool for reworking stacked devices as a whole in a single reflow process. It uses vacuum-actuated mechanical clamping tweezers which avoid separating the single layers of a PoP during component removal. The PoP soldering head can be easily adapted to different component thicknesses. Furthermore it is possible to adjust the width of the clamping tweezers prior to the process when the rework arm is swiveled down to avoid affecting other components on the PCB (e.g. accidental shifting of neighboring small passives).”

Sounds like this would be great for combating “PoP Quicksand”. That nasty problem that large components have when the vacuum provided by the nozzle isn’t strong enough to lift the package-on-package component back out of the PoP solder paste or dipping flux. Okay, I just made up that term – but it’s pretty descriptive, right?

Conceptually it seems to make a lot of sense, please comment if you have any experience with it!

7:40am

Just got in, fired up the laptop, and made some hot chocolate. This is the best time to get a jump on the day. I clear out my spam that rolled in overnight and prioritize the emails in my inbox. The first tasks that I cleared were:

-         Connected a new potential solar materials rep with the right people at Indium Corporation

-         Recommended the optimal reflow profile for Indium9.88HF PoP solder paste

-         Activated an online Vapor Deposition course

-         Helped specify tabbing ribbon and solder wire for a college student working on a lunar rover project

-         Planned underfill testing for today.

10:00am

After rounding up materials, components, and equipment, Brandon Judd and I assembled some BGAs on a customer's test board. Later today we’ll underfill, and rework some of the components to demonstrate the yield of a reworkable underfill. Each board had 18 components of 2 types. One of them is a very large, coarse pitch BGA. The other one (you guessed it) is exactly the opposite, a small, fine pitch BGA.

Noon

Took a drive and ate lunch.

1:00pm

When I returned to my desk, I noticed a few emails that needed attention. One was regarding the PoP solder paste reflow profile I mentioned earlier. It looks like that will work for the particular application. Another email regarded a barcode design that I am working on for a customer.

1:30pm

Took a call regarding solder sphere attachment. WS3622 was recommended to ease flux cleaning in place of an older tacky flux.

2:00pm

Answered an interesting call regarding thermal management for a cavity CPV assembly. The coolest part – he found my contact information on this blog.   

2:45pm

Worked on editing an interview for Global Solar Technology magazine. I had a chance to discuss many of our solar products in detail, while explaining the advantages of each.

3:00pm

The schedule for the day shifted, so we will reconvene the underfill testing early next week.  This gives me some time to begin the Interfacial Engineering course mentioned earlier. Looks pretty interesting so far.  Spent some time going through the course material and learning some new things.

4:30pm

Posted this blog entry. After looking at the things I’ve mentioned here, I noticed I could tweet all the little parts of my day. If you’re interested, check: http://twitter.com/SolderNinja

In an earlier post, I mentioned how hard it was to get technical support from some equipment vendors.  In response to that, Ed Zamborsky (OK International) not only offered technical support, but offered to help answer some of my questions for this blog post.  Cool!

So here is my question: Which iron tips should our customers use for non-standard alloys?  I’m interested in 52In/48Sn, 58Bi/42Sn, 100%In, and 92.5Pb/5Sn/2.5Ag…

Ed: “So much of the tip temperature is dependent upon the target PCB area as well as the mass of the components being soldered. Using a Smartheat soldering system I would suggest the following cartridges for our different systems:

Solder Melt Temperature                         MX Series      PS Series       MFR Series

52In/48Sn (118degC melt)                      500 Series     T Series        T Series

58Bi/42Sn (138degC melt)                       500 Series     T Series        T Series

In (157degC melt)                                 600 Series     F Series        F Series

92.5Pb/5Sn/2.5Ag (287degC melt)            600 Series     F series         F Series

On a heavy substrate or ground plane, you can always select the next higher temperature series to optimize the hand soldering process.“
 
Ed also guided me to a collection of technical videos that he helps put together to assit customers during selection, testing, and use of his company's products - which include rework and dispensing equipment. 

Ed Zamborsky is a product manager for OK International, he can be reached at:

ezamborsky@okinternational.com

386 846 5647

Solder Basics...  If I needed to pick my favorite flux for hand soldering, it would easily be PoP Flux 030B.  I know it’s probably never going to find itself in household soldering toolkits, it’s a semiconductor packaging material – most people never need that good of a flux around the house, but I said it was my favorite, not the most practical. 

This is why PoP Flux 030B is the best choice around the house:

1) It has proven it’s solderability to ENIG, silver, oxidized copper, OSP, and nickel with Pb free and Sn/Pb alloys (which I’d choose any day for my personal soldering applications).

2) It is a halogen free, no-clean flux, so you can just leave it on the pipes, connectors, or stereo wires you’re connecting.

3) It is safe to use even if it isn’t completely heated and cured – this is rare for a no-clean flux.

4) The airless packaging process gives it a unique tack/viscosity ratio and a smooth texture that you just don’t get with cheapo off-the-store-shelf fluxes.

5) It activates at a relatively low temperature but can endure ~300degC reflow.  Hand soldering is not accurate, so I like the widened process window.

6) I think it’s pretty cool to use such an advanced flux for low-tech soldering, it’s overkill at its finest.

 This is a rare photo taken in the underground Structural Solder Joint Test Facility (SSJTF) nearly 5 miles below a small farming town in Central NY.  The light that you see is not really just a cellar window…

A reader of this blog recently mentioned: "I am interested in what products could be sold by manufacturer's representatives."  That is a large question, considering the evolution that we have come to expect in the solar industry.  To answer that question involves first breaking up the industry into 2 separate sections, front and back end solar assembly.  Front end assembly involves the process of making the solar cell.  Back end involves connecting cells together and assembling them to create a useable device.

Both front and back end products are going to be geared to the customer's technology.  For instance, if I was purchasing materials for a large thin-film manufacturing company and someone boldly offered me glass filled high-temperature metallization paste, I would tell them to come back when they know what they are talking about.  (In reality, I'd be nice – even though it's an incredibly ignorant mistake.)  With that in mind, let's focus on what back end products a representative might be offering for crystalline and thin film solar customers – assuming that back end begins after metallization:

• Outsourced Solar Cells
• Tabbing Ribbon
• Bus Ribbon
• Tabbing Flux
• Solder Paste
• Preforms
• Solder Wire
• Tacky-type Fluxes
• Tabbing Equipment
• Rework Equipment
• Test Equipment/Services
• Packaging Materials
• Junction Boxes
• Laminate Materials
• Silicone/Sealing Materials
• Passive Components
• Ovens
• Frames
• Gloves / Lab Coats / Safety Equipment

I probably left out as many possible line items as I included, but I hope you get the idea.  Feel free to add the ones I forgot in the comment section below.

~Jim

Brandon Judd and I have been working on a paper for this year’s SMTAI event, and I thought I would share a snip from it.  Although people generally share the beginning of a paper, I’d like to share the conclusion, in Brandon’s words:

“With the miniaturization of today’s electronic devices and the increasing complexity of their features, the need for PoP components is significantly increasing.  Although it may seem like a simple solution to just use the standard SMT paste that you have in-house for your upcoming PoP applications, these products will not be optimal for this type of process.  As our testing has shown, modern PoP solder paste materials are much better suited to the dipping process used for PoP components.  Formulation, particle size, and metal loading are all key factors in the design of a PoP specific paste.  The time spent evaluating these new products is well worth saving yourself the headaches of getting electrical opens on your boards from using standard SMT materials or even outdated dipping pastes, causing costly and time consuming rework down the road.  With the proper material and process, insufficient solder transfer and head-in-pillow defects should be a thing of the past.  “   

Folks,

Recently someone asked me about reworking a SAC305 solder joint with a SnBi solder. The reason to consider SnBi was that the lower melting point of SnBi would make the rework process easier. The main concern the person had was what the properties of the reworked solder joint would be. Unfortunately no one can tell them. Note that I didn't say that there would be a problem, I just said that the properties of the resulting solder would be unknown. Let's see why.

Cheers,

Dr. Ron

The photo above shows a SnBiPb ternary phase resulting from mixing leaded and Bi containing solders.  This phase has very poor mechanical properties as can be seen in the photo, which is taken after thermal cycling. The photo is from Zequn Mei, Fay Hua, and Judy Glazer, "SN-BI-X SOLDERS", SMTA International, San Jose, CA, Sept. 13-17, 1999.

Proper solder joints provide mechanical, electrical, and thermal interconnections that are reliable over the course of a product’s lifespan.  Unreliable interconnections not only cause product failure, but extend the products time-to-market, cause recall/redesign issues, and increase the amount of rework and line maintenance necessary to keep up with product demand.

Successfully forming a solder joint in most situations is easy, although demanding applications often call for unique alloys, difficult surface finishes, and non-recommended reflow windows.  If you are struggling with these types of issues, searching the internet may not be the fastest way to find a solution.  Send us a question at askus@indium.com or call (315) 853-4900 for a much more custom fit answer to your one-of-a-kind problem.  

What’s the difference between Package-on-Package (PoP) / BGA rework solder paste, and solder paste designed for SMT?  Solder paste for dipping applications is designed to transfer more solder based on its rheological characteristics.  In the chart shown here, a typical SMT paste is compared to 3 next generation dipping pastes.  Although the names cannot be released right now, all PoP/rework pastes transferred over 100% more paste to the solder joint area.  (Hint: you can probably break me down relatively easily if you have me on the phone.  For the whole story call me at (315) 853-4900)

This added solder volume helps ensure that more solder is available during joint formation to compensate for component warpage.  During rework, increased solder volume replaces solder that has been scavenged during the component removal process.  Either way, more solder volume relates to a more robust solder joint.

• Are you looking for information on semiconductor packaging materials?  Send your request to jhisert@indium.com.  It’s all fair game – released, experimental, or competitor materials.  Flux characteristics, paste properties, application methods…

   

  Inquire about any of the following topics:

  • Pin transfer
  • Package-on-Package (PoP)
  • Solder spheres
  • Glass transition temperatures (Tg)
  • Flip chip assembly
  • BGA rework
  • Cross-sectioning electronic components
  • Paste for component dipping
  • Solder alloys
  • Liquid fluxes
  • Wafer bumping
  • Low alpha solder
  • Spin coating
  • Redistribution layers (rdl)
  • Halogen-free
  • Flux viscosity
  • Solder paste viscosity
  • Whatever else you are interested in

 

From a mechanical perspective, larger solder joints are generally preferred when assembling package-on-package (PoP) components.  Just as a large set of gears can handle more power, fortified interconnects add a measure of reliability to BGAs and CSPs.  That is why in many cases, dipping paste is used instead of PoP flux for package-on-package stacking and BGA rework - to increase solder joint volume.  The added volume of solder helps keep the solder spheres in contact with interconnect pads throughout the reflow cycle, combating the effects of warpage.  This will help you increase the solder reliability and the final yield of your PoP assemblies.

Here are some links to learn more about the PoP solder paste process:

Control Your Materials, or They Will Control You (part 1)

Control Your Materials, or They Will Control You (part 2)

Package-on-Package Paste Leveling (1/5)

Package-on-Package Component Dipping (2/5)

Package-on-Package Placement (3/5)

Package-on-Package Transport (4/5)

Package-on-Package Reflow (5/5)