Technical Articles

Effect of Under-stencil Wipe Chemistry on Print Performance

Can a change of solvent in the printer improve SMT printing?

ANY ENGINEER WILL TESTIFY lab testing may not correlate with field results. Laboratory data are developed under ideal conditions to generate accurate and repeatable data, whereas a production setting introduces variables not reproducible in the lab environment.

In this report, AIM’s application lab approximated a production environment in a multi-hour printing test to quantify the effect of under-stencil wipe solvent on solder paste performance. This experiment compared isopropyl alcohol (IPA) and a novel stencil cleaner. IPA is not recommended as an in-process stencil cleaner, but is often used because it is inexpensive, effective and readily available. However, IPA is not a constituent of solder pastes and can therefore cause changes to paste that will negatively impact performance.

One example of this change is that paste exposed to IPA can become...

Mr. Clean

Picking the right tool to prevent electrochemical contaimination at the rework bench.

A half-dozen versions of the same scenario occurred in the past month, all having to do with materials and processes used in post-op/rework applications. This step of the production process often escapes the attention of engineers because there’s no cool machinery or any real engineering that takes place. Most hand-solder operators are highly proficient and have developed techniques that get the job done, which can lull a supervisor or production manager into a false sense of...

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Is SMT Ready for Low-Temperature Solders?

With no standard in sight, emerging alloys require unique fluxes and processes.

LOW-TEMPERATURE SOLDERING is a subject of considerable interest and development. Several forces are driving implementation of solders with lower peak reflow temperatures than SAC 305 and its variants. The most technically significant is reduced warping of component and substrates. Chip suppliers are particularly interested in lower reflow temperatures, as thinner components are needed to meet dimensional limitations of thinner, smaller and faster devices. When a component deforms during reflow, the solder interconnect may be compromised, resulting in non-wet opens (NWO). NWO defects are difficult to detect and may not manifest until after a product is in the field. Other advantages of low-temperature soldering include the incorporation of lower-cost plastics, component and laminate materials, and reduced energy consumption and related environmental...

Solder Paste is Dumb

Could vendor collaboration get to the root cause of an intermittent soldering problem?

Simply put, the ultimate function of a PCB assembly line is to create millions of solder joints without error. This task is complicated by the myriad materials that come together during assembly, and relies on the quality of each lead, pad and sphere to be soldered. When a soldering defect is discovered, it is common practice to presume the soldering materials are the cause, which seems logical, considering it is a solder defect. This assumption is often misplaced. This scenario plays out regularly, as illustrated in a recent case submitted to our failure analysis team for diagnosis.

In this case, the assembler had an intermittent solderability issue with a component. It brought the problem to its local representative’s attention on several occasions. The issue was...

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Profiles in Expertise

Is reflow the only process where the outcome could be impacted in real-time?

One of AIM’s field engineers came back from a cross-country trip this week with stories of a profiling issue that was giving the client difficulties. Ultimately, the issue was design-related with a large ΔT that could not be overcome with the equipment used in production. It took a full day of attempts to make that final assessment. 

Many engineers and technicians I work with rank reflow profiling alongside getting their teeth cleaned or an early morning workout. You know you need to do it, and the benefits are significant, but they aren’t immediate, and it is an unpleasant chore. Let’s take a minute to go over best practices for reflow profiling. Ideally, a “golden board” will have been supplied as part of the work kit by your customer or your design team. This...

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