PCB Baking: Should Expired Circuit Boards Be Baked? A 4-Step Decision Process

Whether to bake a PCB is not decided by the date alone; check four things in order: whether the vacuum pack has been opened, whether the humidity indicator card (HIC) has changed color, what the surface finish is, and whether the shelf life has passed. Boards with intact packaging and a normal humidity card usually need no baking; bake just when they are confirmed to have absorbed moisture, and ask the board maker first for OSP, immersion silver and immersion tin boards, which are sensitive to heat. Baking deals with moisture alone and cannot rescue oxidized pads, so expired boards still need a solder trial after baking before you decide whether to use them.

Figure 1. Should an expired PCB be baked? A 4-step decision process. Start: a stack of PCBs stored too long. ① Has the vacuum pack or moisture barrier bag been opened or damaged? If not, go to ②; if so, go to ③. ② Has the humidity indicator card passed the point the board maker specifies? If not, no baking is needed; if so, go to ③. ③ What is the surface finish? HASL or ENIG: bake to the board maker’s conditions (sources differ; see Table 1). OSP, immersion silver or immersion tin: ask the board maker first; general baking is not recommended; if baking is unavoidable, lower the temperature, bake a small trial batch and test-solder. Unsure: check the shipping documents or ask the board maker. ④ Has the board maker’s labeled shelf life passed? If not, put the boards on the line soon, storing them after baking as in Table 2. If so, baking deals with moisture alone, so run a small solder trial or solderability check: pass, use on the line; fail, consult the board maker or scrap. Conditions and shelf life follow the board maker’s documents and customer specifications.

Table 1 | Baking notes by surface finish

ZVEI is the German Electrical and Electronic Manufacturers’ Association. Standard content is quoted from publicly reproduced or cited excerpts alone; the standard texts were not seen. Figures are for reference; this describes the general case, and individual cases still need their own assessment.

Table 2 | Storage and re-exposure time after baking (just the cells with a traceable source)

The first two rows disagree (24 hours vs. 8–12 hours); this article does not pick one for you; follow the board maker’s rules and your own validation.

1. An expired PCB can fail in three ways, and baking addresses one

• Moisture: resin laminate absorbs water, which expands during reflow and may cause inner-layer delamination and blistering. The scope of IPC-1602 (the standard for board handling and storage, issued 2020, replacing IPC-1601A) points to this risk; lead-free processes run hotter, so the risk is higher.
• Surface finish aging: HASL, ENIG, OSP and other pad finishes oxidize over time, which is why there is a “shelf life.”
• Intermetallic (IMC) growth: heat and time thicken it, and once it reaches the surface and oxidizes, it is harder to wet.

Baking addresses just the first; it does not help the second or third, and several sources say it actually accelerates them.

PCBs are also not covered by J-STD-033, whose scope is non-hermetic surface-mount devices (SMDs). Board moisture is managed by moisture content, commonly 0.1% to 0.5% of resin weight. For component MSL, see “What is MSL for moisture-sensitive components? J-STD-033 packaging, exposure time and baking.”

2. Steps 1–2: check the packaging and humidity card before reaching for the oven

The dry packaging IPC-1602 describes seals the boards in a moisture barrier bag (MBB) with desiccant and a humidity indicator card. In a 2022 industry expert Q&A, most respondents held that if the seal is intact and the humidity card shows no obvious color change, no baking is needed; consider baking just when the seal has failed or the card has clearly changed color.

But there is a differing view: one board maker’s technical advice is that epoxy laminate is not very absorbent and need not always be baked, but baking is recommended after 6 months, after the pack has been opened, or when moisture is suspected. The first view looks at packaging condition; the second also counts time. Where customer specifications or the board maker’s shipping documents say otherwise, follow them; this describes the general case, and individual cases still need their own assessment.

Read the humidity card at the point the board maker specifies; in the expert Q&A, a common threshold is 10% RH or below as normal. The card reflects the environment inside the bag, not the moisture content inside the board, so it is a proxy. The product page for our blue six-spot humidity indicator card gives a range of 10% to 60%, with colors that recover after drying; but if the 60% spot changes color, the card should not be reused.

How long can boards sit after opening? The IPC-1602 catalog and comments we found have no table of “level vs. exposure time” like component MSL, so do not apply component MSL times to boards; ask the board maker for the maximum exposure time after opening.

3. Step 3: if you must bake, how to set the conditions

There is no single set of figures for the whole industry. IPC-1601A’s table lists 105–125 °C for 4–6 hours (as reproduced by ZVEI) and notes that the user must validate conditions for the board type, and clause 3.4.4 of IPC-1602 (also as reproduced by ZVEI) likewise leaves validation to the user; one board maker recommends 120 °C for about 2 hours for HASL and ENIG; among industry experts, one says 125 °C harms solderability and 105 °C is a general-purpose temperature, while another bakes 2 mm boards at 110 °C for 4 hours, or at 93 °C for 8 hours. Another source paraphrases IPC-1601A as saying the temperature should be below the laminate’s Tg (one source alone). The common trend: the higher the temperature, the more the surface is harmed; the thicker the board, the slower it dries.

Loading: the oven should be clean, with space between boards for hot air to circulate (board maker’s technical document). Baking can also warp boards: a European study found every board type warped at 130 °C, and an expert also warns that pre-baking can cause warpage, so check flatness after baking. Sources give no consistent figure for how many boards may be stacked, so this article gives none.

How many times: there is no standard figure. Several experts agree: bake as little as possible, since repeated baking adds oxidation and thickens the intermetallic layer.

If you need an oven with programmable ramps, our JHSXH-480 smart programmable oven lists PCBA and IC baking among its uses, with programmable temperature profiles and a nitrogen purge line; the temperature range and chamber size are not on the page, so please ask.

4. Does baking improve solderability? Every source we found says no

Baking drives out moisture to prevent delamination in reflow; it does not make pads easier to solder. The board maker’s document, the ZVEI comments and the expert answers we found all treat baking as accelerated aging: the board maker says baking is a form of aging that may reduce solderability; ZVEI says it artificially ages the solderable surface and recommends baking just before soldering; an article citing IPC-1601A says baking at 125 °C for 4–6 hours may make HASL boards unsolderable; and an expert points out that baking accelerates intermetallic growth, which, depending on plating thickness, may reach the surface and make it hard to solder.

We found no standard or board maker document supporting “baking improves solderability.” To check, run one group baked and one not from the same lot, and go by your own results.

5. OSP, immersion silver and immersion tin: why the advice differs

• Not recommended: one board maker lists these three as “very sensitive”; IPC-1601A recommends not baking OSP boards; experts also say baking degrades the OSP layer.
• If unavoidable: use the lowest temperature and a short time, bake a small batch first, test-solder it, scale up if it passes, and bake just the quantity about to go on the line. The board maker, experts and the board maker’s blog agree on this.
• The dispute is over figures: the standards and board maker documents we found give no validated baking temperature and time for OSP boards; figures circulating online have no standard source and differ from one another. So this article gives no figures. This describes the general case; ask the board maker or OSP chemistry supplier first.
• Another route: dehumidify slowly at about 40–60 °C and below 1% RH, over tens to hundreds of hours; ask the board maker first whether this suits your boards.
• Immersion silver packaging must contain no sulfur and be pH-neutral.

6. After baking: how soon to use them, and how to store them

Baked boards reabsorb moisture, and the sources agree: use them as soon as possible after baking, and bake just the quantity about to go on the line (see Table 2). How soon “as soon as possible” is differs between sources, and this article does not pick one for you.

Boards not used should be resealed in dry packaging: a moisture barrier bag, desiccant and humidity indicator card together. IPC-1602 defines the moisture barrier bag as including a metallized aluminum layer (shiny, opaque), and ZVEI also notes that transparent non-metal plastic bags are unsuitable; pulling a full vacuum may actually weaken the desiccant. For bags, see our aluminum foil bags (antistatic), and for choosing a bag type, see “How to choose ESD bags.” Boards not used that day that you don’t want to reseal can be held in a low-humidity environment, such as our ultra-low-humidity electronic dry cabinets (the product page lists two grades, 1%–10% RH and 1%–3% RH; please ask whether they suit your boards).

7. Step 4: past shelf life, is baking enough?

No. Shelf life is about solderability, and baking is about moisture: two separate things. The sources we found roughly put HASL and ENIG around 12 months and OSP, immersion silver and immersion tin around 6 months (see Table 1), but their figures do not fully agree, so follow the board maker’s label. Baking also does not reset the shelf life: one expert states that baking cannot restore shelf life and instead accelerates intermetallic growth.

For expired boards, we suggest:

1. Inspect: check whether pads have darkened, corroded or roughened.
2. Small solder trial: run a few boards through your actual process and check wetting.
3. For formal data: run a solderability test to IPC J-STD-003 (solderability tests for printed boards).
4. Release the whole lot just after the trial passes: if it fails, discuss with the board maker or scrap; do not force it onto the line. Baked boards go through this step too.

Related reading

• “What is MSL for moisture-sensitive components? J-STD-033 packaging, exposure time and baking” (components such as ICs and connectors)
• “How to choose ESD bags: antistatic, conductive and shielding, and when foil bags are needed” (bag types for resealing after baking)
• “Dry cabinets vs. nitrogen cabinets: 4 selection points for storing moisture-sensitive items”
• “What is the popcorn effect? Why moisture in ICs and boards makes them crack in reflow”

Products mentioned in this article

Specifications follow each product page; please ask for configuration, price and lead time.

• JHSXH-480 smart programmable oven: programmable temperature profiles; please ask for temperature range and chamber size.
• Blue six-spot humidity indicator card: six spots, labeled range 10% to 60%, colors recover after drying.
• Aluminum foil bags (antistatic): for resealing after baking; see the product page for specifications.
• Ultra-low-humidity electronic dry cabinets: the product page lists two humidity grades, 1%–10% RH and 1%–3% RH.

For baking equipment selection, humidity indicator cards or moisture barrier packaging, contact JIAHON.

Standard sources

For the standards cited, refer to each publisher’s current edition.

• IPC-1602, Standard for Printed Board Handling and Storage, published by IPC (Global Electronics Association)
• IPC-1601A, Printed Board Handling and Storage Guidelines, published by IPC (Global Electronics Association)
• ZVEI, Recommendations/comments on IPC-1602 (August 2022), published by ZVEI
• ZVEI, Recommendations to IPC-1601 (June 2021), published by ZVEI
• IPC/JEDEC J-STD-033, Handling, Packing, Shipping and Use of Moisture, Reflow, and Process Sensitive Devices, published by IPC (Global Electronics Association) and JEDEC
• IPC J-STD-003, Solderability Tests for Printed Boards, published by IPC (Global Electronics Association)

This article is a summary of the general case, not a restatement of any standard, and not an endorsement of your process. Follow the board maker’s shipping documents, customer specifications and your own validation for baking conditions and shelf life; this describes the general case, and individual cases still need their own assessment.

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