The Chargers Passed Inspection, Then Died Six Weeks Later
A Guide to Electronics Aging and Burn-In Testing - Why Electronics Fail Early, Room-Temperature and High-Temperature Aging, On/Off Cycling, HTOL, Damp Heat and Temperature Cycling Compared, Function and Hi-Pot Checks Before and After Aging, Time, Temperature, Load and Record Spec Items, Rack Capacity, Checks at Sample, Production and Shipment, Request Wording, Real Cases and a Checklist

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An online brand selling small electronics and accessories had a factory in Shenzhen produce 5,000 65W USB-C fast chargers. The samples ran cool and charged quickly, so mass production was approved right away, and the pre-shipment inspection, which plugged units in and checked that they charged, found zero defects. Six weeks into sales, though, messages started coming in: "One day it just stopped turning on," and "It clicked while I was using it and died." Over three months, 190 units came back with the same symptom, about 3.8% of sales.

Taking the failed units apart, the team found the same thing again and again: a swollen electrolytic capacitor, or a cold solder joint on a MOSFET lead. When asked, the factory admitted the problem was in its aging test (老化测试). The process was supposed to run each finished unit under rated load for 4 hours, but to hit the deadline the factory cut it to 30 minutes and skipped it entirely for the last two lots. The purchase order said only "老化测试" (aging test). Nowhere did it say how many hours, at what temperature or under what load.

Aging is the step that weeds out early failures before shipment. Routine inspection only checks whether a unit works right now, so it cannot catch units that will die in a few days or weeks. This article covers why electronics fail in a cluster early in their life, what aging and burn-in tests are and how to set the conditions, and what to put in your spec and on-site checks.

Early failures show up in a cluster within weeks of reaching the customer. Set aging time, temperature, load and before-and-after checks as numbers, and confirm from records that the factory actually ran them.

1. Why Electronics Fail Early

Plot a product's failure rate over time and you get the shape of a bathtub. Reliability engineers call it the "bathtub curve." The failure rate starts high, drops quickly, stays low for a long stretch, and climbs again as the product wears out. Aging pushes units through that early-failure stretch inside the factory. These are the causes of early failure we see most often.

• Bad solder joints (虚焊·冷焊): A joint that looks attached but is not properly bonded breaks apart after repeated heating and cooling. It is especially common on the leads of heavy or hot-running parts.
• Component variation: Capacitors, diodes and ICs of the same rating still include weak units depending on the lot. Cheap or untraceable parts raise the share.
• Electrolytic capacitors: Capacitors without enough temperature or voltage margin degrade quickly in products that run warm. Once they swell or leak, the power stage stops.
• Assembly and fastening defects: A connector that is only half seated or a screw that is under-torqued loses contact after a few rounds of vibration and temperature change.
• Firmware and protection circuits: Firmware that misbehaves only at certain temperatures or loads does not show up in a short function test.

For a factory, aging eats time, floor space and electricity. The number of aging racks (老化架) is fixed, so when output peaks, the temptation to shorten or skip aging grows. It is not unusual for a factory to run aging properly for samples and then quietly cut it during a rushed production run. You can't tell the difference by looking at the finished product, so tie the conditions and records down in writing.

2. Types of Aging and Key Tests

"Aging" covers several different methods. Aging done on every unit during production and reliability tests run on a handful of samples to check lifetime and durability serve different purposes, so request them separately.

Common Conditions by Product

Chargers and adapters are often aged at 80-100% of rated output for 2-4 hours at room temperature or 40-45°C, and LED lighting is commonly left lit for 4-8 hours. Products with batteries, such as power banks, usually run one or two charge-discharge cycles, while small appliances with motors combine continuous running with on/off cycling. These are only starting points. The actual conditions get adjusted based on failure history and cost.

We covered importing LED lighting and home appliances in Episode 78 and Episode 75, and lithium battery products in Episode 90. This article focuses on the step that screens out early failures before shipment.

3. What to Check Before and After Aging

Aging is not just leaving units plugged in. Weak units only show up when you measure the same items before and after aging and compare. If the factory treats aging as "pass if it turns on," half the value of aging is lost.

• Function test: Output voltage and current, fast-charge protocol recognition, buttons and indicator lights
• Electrical safety: Hi-pot (耐压), insulation resistance and ground resistance tests. The rule is to repeat them after aging.
• Temperature: Record surface and key component temperatures during aging
• Warning signs: Noise, smell, flicker, unstable output

Units that shut down during aging should not just be pulled and thrown away. Have the factory record the quantity and the failed part. A sudden jump in the aging failure rate signals a problem with a component lot or the soldering process, and that data becomes your evidence when you later ask for root cause analysis and corrective action. See Episode 122 for how corrective action reports work.

4. Spec Items That Make Aging Actually Happen

The four characters "老化测试" don't tell the factory how long or under what conditions to run it. Write the conditions, pass criteria and record format down as numbers.

See Episode 59 for spec sheets in general. Work out the rack capacity yourself, too. With 100 units per rack and 4-hour aging, one rack running two shifts a day handles about 400 units. If the factory's promised daily output is larger than its rack capacity, there is a good chance it is cutting aging time.

5. How to Check at Each Stage

Sample Stage

Take a few samples and run them continuously at rated load for a day or two at home or in the office. For a charger, leave a laptop connected; for a light, just leave it on. It costs nothing, yet it tells you a lot about heat and early-failure tendencies. If your sales channel or certification requires it, send samples to a lab for reliability tests such as damp heat and temperature cycling.

First Article and Production Stage

Agreeing on aging conditions, rack count and the log format at the pre-production meeting makes everything after much easier. We covered this in Episode 123. Once production starts, ask for photos or video of the aging area to confirm the racks are actually running. Comparing the number of units on the racks with that day's output gives you a rough idea of whether aging is really happening.

Pre-Shipment Inspection Stage

Have the inspector cross-check the aging log for each lot, and put a few samples back under load on site for 1-2 hours. If the dates and times in the log don't match the production schedule, or every lot shows exactly zero failures, it is worth a closer look. See Episode 100 for pre-shipment inspection.

6. Sample Request Wording for the Factory

Putting the wording below in your purchase order or spec makes it harder for the factory to cut aging, and leaves a basis for assigning responsibility if early failures appear.

"本产品成品须100%进行老化测试：输入电压220V，带额定输出90%负载，环境温度40±5℃，持续4小时；老化期间每30分钟开关机一次。老化前后须进行功能测试（输出电压、电流、快充协议识别），老化后须进行耐压测试。老化中出现的不良品须单独隔离并记录数量和不良现象，单批老化不良率超过1%须立即通知我方。每批须提供老化记录表（批号、上架和下架时间、老化架编号、温度、不良数量）。电解电容须使用105℃规格并采用双方确认的品牌。如需更改关键元器件、PCB供应商或老化条件，须事先取得我方书面确认。"
(Every finished unit of this product must undergo aging: 220V input, 90% of rated output load, ambient temperature 40±5°C, for 4 hours, with power cycled once every 30 minutes during aging. A function test (output voltage, current, fast-charge protocol recognition) must be done before and after aging, and a hi-pot test after aging. Units that fail during aging must be isolated, with quantity and failure symptoms recorded, and you must notify us immediately if the aging failure rate of any lot exceeds 1%. Provide an aging log for each lot (lot number, rack-in and rack-out time, rack number, temperature, failure count). Electrolytic capacitors must be rated 105°C and from a brand confirmed by both parties. Any change to key components, PCB suppliers or aging conditions requires our written approval in advance.)

7. Three Real Cases

These are anonymized versions of situations we often see in consultations. Amounts and figures are examples.

Case 1 — 65W USB-C Chargers

This is the case from the opening. Aging the remaining 300 units in stock at 40°C under rated load for 4 hours, 11 of them shut down. From the next production run, aging conditions and submission of aging logs went into the spec, and the electrolytic capacitors were switched to a 105°C-rated branded part. Unit cost rose by about RMB 0.6, a small amount next to return shipping and replacement costs. Over the following three months, returns for the same symptom fell to around 0.3%.

Case 2 — LED Mood Lights

The factory said it had done aging and sent logs, but every lot showed zero failures and the rack-in time was identical every day. An inspector visited and found a single aging rack holding 20 units, against daily output of 1,500. The logs had been filled in for show. Only after more racks were added and the factory began sending daily video of the racks in operation did early lighting-failure claims drop.

Case 3 — Rechargeable Mini Fans

Finished-unit aging was done properly, yet returns saying "it won't charge" rose during the summer peak. It turned out aging only ran the motor at room temperature, and the charging circuit was never aged at all. After one charge-discharge cycle was added to aging and the soldering around the charging IC was reinforced, the same failure fell noticeably. Aging conditions need to follow how the product is actually used.

8. Common Mistakes

• Writing only "老化测试" on the purchase order without setting time, temperature or load
• Passing units after aging just because they turn on, without comparing before-and-after readings
• Not comparing rack capacity with daily output
• Receiving aging logs without cross-checking what they say
• Aging only part of the product's functions, such as the motor but not the charging circuit
• Not confirming that the components used in samples are still used in production

9. Aging and Burn-In Checklist

Spec and Contract Stage

• Aging scope (100% or not), time, temperature and load are in the spec
• Before-and-after test items and tolerances are defined
• A notification threshold for the aging failure rate is included
• Key component ratings and a change approval clause are included

Sample and First Article Stage

• Samples were run continuously at rated load for at least a day
• The factory's aging rack count was compared with daily output
• Both sides agreed on the aging log format

Production and Shipment Stage

• Photos or video of the aging area confirmed the racks were running
• Aging logs for each lot were checked against the production schedule
• Pre-shipment inspection included re-aging of samples and a hi-pot test

Wrapping Up - Start by Leaving One Sample Running for a Day

Of all quality problems in electronics, early failure leaves the longest-lasting mark on a brand. When a unit that passed inspection dies in the customer's hands within weeks, the customer doubts the brand, not just the product. Once you count returns, replacements and falling ratings, doing aging properly is not expensive.

There is something you can do right now. If you have stock or samples, take a few out and leave them running at rated load for a day. If any shut down partway or get too hot to touch, reset your aging conditions and component specs before the next order.

StartMade supports you on the ground with spec sheets that include aging conditions, checks of factory aging equipment and rack capacity, cross-checking of aging logs per lot, and on-site re-aging during pre-shipment inspection. If early-failure claims have already started, we begin with root cause analysis; if you are preparing a new product, we start with the aging criteria.