Ask the Experts
August 18, 2017 - Updated
July 4, 2007 - Originally Posted

Solder Paste Inspection

Our Company is adding a new SMT assembly line and needs to decide on a solder paste inspection system based on a customer request. After leaving the APEX show, we saw several options, including inspection on a screen printer or a dedicated AOI solder paste inspection system. I also thought I saw a Pick and Place system with solder paste inspection or alignment, but could not remember which company? Can you offer any suggestions for a new solder paste inspection system for a small SMT subcontractor?


Expert Panel Responses

As you observed, there are paste inspection solutions to meet every need. Focusing on the "need" should guide you to the solution that is best for your products and organization. What are you trying to accomplish by doing solder paste inspection? Data shows that solder paste volume is linked to long-term joint reliability. If reliability and quality are your drivers, you should investigate a 3D solder paste inspection system. At this point in time, there are automated solutions that can keep up with any beat-rate or be used off-line for smaller builds. The quality of data-output and your plans for that data should be a big driver in your decision making. It is hard to provide a complete answer on all of your options without more information on what you are trying to accomplish but there are many companies that have several offerings. If you speak to a contact within those organizations they should be able to point you to the solution and implementation that is best for you.

Stacy Kalisz Johnson
Americas Marketing Development Manager
Agilent Technologies
Ms. Johnson's entry into the electronic packaging arena was as a Package Development Engineer. Stacy recently joined the Americas Field Marketing Organization as a Marketing Development Manager for the Americas where she continues to work on AOI, AXI and also In-Circuit Test.
NOTE: Ms. Johnson is no longer working at Agilent Technologies.

In answer to your question I would like to offer the following input: Solder paste inspection as with any AOI applications is very application dependent. There is no one solution for any aspects of Automated Optical Inspection whether it be Solder Paste, Pre-Reflow or Post Reflow inspection. Specifically for Solder Paste inspection, the first question to ask is whether you require 2D inspection using a camera or 3D inspection which normally users a laser. This depends on the component sizes and paste deposition required. If you are not placing any 0.4mm BGA's or 0201 Components then 2D is sufficient, below these pad sizes 3D may be the best option. Most systems that are integrated into the screen printer are 2D inspection systems and are relatively slow. They also tend to be selective measurement systems, not inspecting the whole board. It is not always a good idea to have the system doing the paste deposition carrying out the inspection as well. 2D inspections systems are much cheaper than 3D systems and a lot less complicated. If paste registration is the main concern then 2D is the way to go. If deposition height and volume is the major issue on smaller components you may need 3D but on anything down to 0402, the transfer levels are very good. Most 3D systems on the market are not accurate but they are repeatable, this is due to the issues relating to laser triangulation and the filters used to get a clean signal. If you need more information or any white papers on these applications do not hesitate to contact me at

Mark Norris
Vice President Asia
Nordson Advanced Technologies
Responsible for Nordson Advanced Technology Electronic Systems throughout Asia including China, Taiwan, Korea, Japan & SE Asia. Nordson Advanced Electronic Systems includes the world leading technology companies Asymtek Dispensing, Dage X-Ray, Dage Bond Test, March Plasma, Matrix AXI & Yestech AOI.

Your first task is to identify your end goal. What is it you, or your customer, what inspected? Then, ask what information or actions you require given the faults your looking for. From there you can filter out the solution that best fits your needs. A knee jerk response to this question may be to say you want " everything", but this is usually not the case. First is the budget. Do you need a Printing Machine solution in the $10-20K range, or an in line 3D solution at $150-200K? But beyond the budget is the task of supporting the tool on your production floor. Will this be an engineering tool for NPI, where an engineering level support is requires to set up and collect extensive data, or is the end goal simply to provide a "go no-go" solution on the production floor that the operator can easily set up and support. If extensive data at high speed is required, then your looking at the hi end 3D systems. If general data, paste present and aperture clog with bridging and stencil smear detection is needed, then the printing machine can offer a less expensive solution. However, this option usually requires an engineering knowledge level for support and will reduce your through put. Another option is a paste verification system on the printer, which simply monitors the print quality and detects if the print quality drops, but does not collect SPC data. This type of inspection is the easiest to set up and support, and has the least effect on your through put. This link will explain this solution in more detail.

Michael O'Hanlon
Applications Supervisor
Mr. O'Hanlon serves as the DEK Applications Supervisor for the Americas region. He has over 20 years of electronics manufacturing experience and has spent the last 13 years at DEK providing equipment utilization and process solutions for SMT manufacturing.

For solder paste height measurements, you can use Cyber Optics Auto LSM.

Peter Greenland
Global Sales Director
Photonis USA
Mr. Greenland has 20 years electronics industry experience ranging from circuit board design to product support & repair services. Peter has spent the last 4 years at Pycon Inc. supporting customers that require high mix, low volume manufacturing solutions.

There are several factors to consider. First you must determine what type of post print inspection you want to implement. Do want to implement two dimensional (2D) or three dimensional (3D) post print inspection? The 2D system will evaluate solder paste/PCB pad converge, the 3D system will evaluate coverage and solder paste volume Evaluating solder paste volume is a more robust method of process control. The second factor is process cycle time. You have to factor how much time you can afford for post print inspection. If you are using the post print inspection system on your printer, your per board cycle time will increase by whatever time you use for post print inspection unless you have the newest innovation in printing equipment which can perform post print inspection and other tasks simultaneously. Once you have determined what and how many solder paste deposits you want to inspect and how you want to inspect them (2D or 3D) then you can evaluate the equipment options. There are many excellent post print inspection systems available today both stand alone in line systems, stand alone batch systems, and systems that are integral to the printing equipment. Whatever system you chose do not forget to perform your Gauge R & R studies to evaluate the capability of the inspection system to measure what it is you want to measure.

Joe Belmonte
Principal Consultant
ITM Consulting
Mr. Belmonte has been a process engineer and process engineering manager in the electronic manufacturing industry for over 25 years, with experience in all aspects of electronic product assembly operations. He is well-known throughout Asia and SE Asia for both his process work and teaching engagements.
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