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'Bump'ing up coverage: a novel soldered probe could improve access at ICT.



Test access continues to be an issue, especially for in-circuit test, which is fundamentally dependent on electrical access. One way to battle the access issue at ICT (1) (Information and Communications Technology) An umbrella term for the information technology field. See IT.

(2) (International Computers and Tabulators) See ICL.

1. (testing) ICT - In Circuit Test.
 is through Bead Probe technology Bead Probe Technology (BPT) gives the electronics industry a new alternative in providing electrical access (called “node access”) to Printed Circuit Board (PCB) circuitry needed to perform In-Circuit Testing (ICT). . This novel method is steadily becoming more mainstream, and the number of licensees increasing rapidly.

Bead Probes enable us to look at test access in a new way. A Bead Probe, which is a soldered Pronounced "sod-erd." Permanently attached by a hard metal bond. In order to replace a chip soldered to a circuit board, it requires heating the soldering joints until they melt. Contrast with socketed.  bump (Figure 1), can be placed directly onto copper signal traces. The bumps bumps

a term used to describe a variety of papulonodular dermatoses in horses, including 'heat bumps', 'feed bumps', 'protein bumps', 'wheat bumps' and others. No specific disease or etiology has been assigned to the term and veterinary dermatologists wish it would disappear from use.
 are added using existing solder paste Solder paste (or solder cream) is a mix of small solder particles and flux. It is used extensively in the automated soldering processes wave soldering and reflow soldering.  printing principles, reflowed using standard procedures, and then serve as the probe test point for ICT access. Beads are layout-independent (i.e., they can be added after copper layout without the need to move or modify traces) and use standard ICT methods. The bumps also merge the world of the process engineer with the test engineer - a long separate bunch of folks! This month, I explore some of the recent discoveries with using these novel bumps in a manufacturing environment. As with anything new, education, experimentation and practice will make perfect.

[FIGURE 1 OMITTED]

The bump locations need to be entered into the design. To do this, users either assign a bump location as pad geometry (normally looks like a via) or assign as a surface mount component. There are board design considerations as well. Keepout areas around components and component outlines need to be validated and respected. That said, costly re-routing of signal paths during layout to accommodate traditional test pads would not be needed. It is important to confirm the CAD denotes openings in the solder mask An insulating pattern applied to a printed circuit board that exposes only the areas to be soldered.  for the bump locations. Commercially available tools exist to automate this with no modifications to copper and with the keepouts and restrictions automatically maintained.

When doing any test and inspection, there are always CAD translation considerations to plan for. The method the layout engineer used to define the bump locations, as mentioned, needs to be known, as well as the side of the board the individual locations have been assigned. As with any utilization of CAD, being able to identify the x-y locations of the bumps will be necessary.

For years process engineers have studied the impact of solder paste types on printability and flux flux

In metallurgy, any substance introduced in the smelting of ores to promote fluidity and to remove objectionable impurities in the form of slag. Limestone is commonly used for this purpose in smelting iron ores.
 residue residue n. in a will, the assets of the estate of a person who has died with a will (died testate) which are left after all specific gifts have been made. Typical language: "I leave the rest, residue and remainder [or just residue] of my estate to my grandchildren. . Ideally the bump print deposition would be inspected using solder paste inspection or AOI AOI Area Of Interest
AOI Automated Optical Inspection
AOI Art of Illusion (3D modeling software)
AOI Associated Oregon Industries
AOI Angle Of Incidence
AOI Age of Innocence (David Hamilton book, also a band) 
 to ensure print robustness and repeatability. In fact, while implementing the bump technology, users can also help identify other process issues. The photos in Figure 2, for example, are from the same board, showing obvious solder solder (sŏd`ər), metal alloy used in the molten state as a metallic binder. The type of solder to be used is determined by the metals to be united. Soft solders are commonly composed of lead and tin and have low melting points. Hard solders (i.  problems causing the issues noted. Flux residue on the bumps may impact contact with the probe. Minimizing residue for bump implementation is necessary and attainable with test friendly solder pastes. Process engineers have worked hand-in-hand with bare board suppliers to keep solder mask tolerances in check. These are now considerations the test engineer needs to investigate when implementing soldered bumps as well.

[FIGURE 2A OMITTED]

Fixture An article in the nature of Personal Property which has been so annexed to the realty that it is regarded as a part of the real property. That which is fixed or attached to something permanently as an appendage and is not removable.  vendors need to be a partner in soldered bump development. Implementation has the potential to change the fixture cost. In some cases, if the bump locations are on the fixture top, costs may increase, but in turn more probing options may reduce fixture cost. Flat-faced probes are ideal. Headed or headless can be used. Headless probes permit guided probe techniques.

[FIGURE 2B OMITTED]

As with any new technology, education is critical for success. Like characterizing a new solder paste or implementing 01005 placement, process design and characterization are a must. Boning up on process engineering skills such as using test-compatible solder paste to minimized flux residue, and working with the bare board manufacturer to keep solder mask opening tolerances, will ease soldered bump implementation. Users need to work with fixture suppliers to ensure proper probe selecting and seating, which are critical. Successful implementation requires synergy The enhanced result of two or more people, groups or organizations working together. In other words, one and one equals three! It comes from the Greek "synergia," which means joint work and cooperative action.  among design, test, fixture, bare board and manufacturing. This synergy will provide an opportunity to opening access and in many cases provide better coverage.

[ILLUSTRATION OMITTED]

Stacy Kalisz Johnson is Americas marketing development manager at Agilent (agilent.com); stacy_johnson@agilent.com.
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Title Annotation:Test and Inspection
Comment:'Bump'ing up coverage: a novel soldered probe could improve access at ICT.(Test and Inspection)
Author:Johnson, Stacy Kalisz
Publication:Circuits Assembly
Date:Oct 1, 2008
Words:674
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