For 01005 parts, some apertures are better than others.

Continuous reduction in component size has been at the forefront of electronics product innovation, assembly process development and the industry conversation for years. Readers will no doubt recall the papers presented, tools developed, and processes modified to accommodate the “coming soon” metric 03015 and 0201 components. That preparation is essential. In my opinion, however, it is more likely than not that widespread use of these ultra-small chips is far in the future; it will come, but probably not in the next generation.

Another reality presents, perhaps, a more immediate challenge: increasing component density beyond current norms. Realistically, for next-generation mobile phones and wearables, the primary consumers of the most miniaturized components, board designs will continue to incorporate the 01005 chip (metric 0402). There are a gracious plenty of reasons for this, not the least of which are cost and component availability. The challenge for product designers is how to get the most function from chips that may be larger than they would prefer. What’s the solution? Squeeze the 01005s closer together, of course!

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Sales pitches from Chinese board shops should come with arthritis medication.

Dramatis PersonaE (in order of appearance):

1. Saleswomen from Chinese printed circuit board fabricators, all with curiously westernized first names.
2. Marketing types trying to sell me lists of attendees at nonexistent trade shows.
3. Serial killers.
4. Clowns (sometimes indistinguishable from #3). Generally speaking, disturbing.
5. SBA-approved loans. (I have one qualified offer right now from capitaldrip.com. I’m not making this up.)
6. Webinars about I-9 forms and Covid-19 mitigation and prevention.
7. Virtual trade shows (and the people lurking behind them).
8. SAM renewal.
9. Persons wanting me to sell our business.
10. Search engine optimization (SEO) companies, which often lead to:
11. Website developers from India named Mike.

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Results of experiments on PTH parts.

Use of low-temperature solders (LTS) is growing in popularity. LTS are predominantly composed of tin and bismuth, with a small quantity of a “special blend” of other elements to suit a given manufacturer’s performance specifications. The opportunity, as the name suggests, is to create solder joints at far lower temperatures than those required for tin/silver/copper (SAC) alloys, and which are even lower than that needed for the (historic?) tin/lead eutectic solder. These LTS have a melting temperature of ~138°C. The benefits of using LTS mean no Pb is present in the joint, and lower processing temperatures can be used. Using lower temperatures means reduced energy consumption during manufacture, lower manufacturing costs and reduced greenhouse emissions. In addition, it offers the opportunity to use different, thinner and possibly cheaper PCB substrates and components compared with those used today. This obviates the “overengineering” required of today’s boards and components to mitigate warpage, which due to LTS are operating close to the glass transition temperature of the board material. It also makes it possible to rework SAC area array package joints with low-temperature alloys.

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Moisture is only one of the potential culprits.

PCB delamination can be subtle or obvious. It is caused by expansion of moisture in the PCB laminate, but that may not be the root cause. Eliminating moisture often prevents the energy buildup that forces apart different layers, but this is not the complete story. Poor bonding during manufacturing of the multilayer board or some form of contamination may result in poor adhesion on innerlayers, permitting moisture to accumulate on these surfaces.

FIGURE 1 shows solder mask cracking around a through via. The PCB expanded during reflow, then contracted during cooling. This resulted in lifting and cracking of the solder mask, plus an intermittent electrical connection. FIGURE 2 shows the innerlayer surface of the board after separation. The through vias are separated and there is no visible adhesion on this layer.

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